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Considerations for reducing food system energy demand while scaling up urban agriculture Article
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Mohareb E Heller M Novak P Goldstein B Fonoll X and Raskin L (2017) Considerations for reducing food system energy demand while scaling up urban agriculture Environmental Research Letters 12 (12) 125004 ISSN 1748shy9326 doi httpsdoiorg1010881748shy9326aa889b Available at httpcentaurreadingacuk74000
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Environmental Research Letters
LETTER bull OPEN ACCESS
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Environ Res Lett 12 (2017) 125004 httpsdoiorg1010881748-9326aa889b
LETTER
Considerations for reducing food system energy demandwhile scaling up urban agriculture
Eugene Mohareb17 Martin Heller2 Paige Novak3 Benjamin Goldstein45 Xavier Fonoll6 andLutgarde Raskin6
1 School of the Built Environment University of Reading Reading United Kingdom2 Center for Sustainable Systems University of Michigan MI United States of America3 Department of Civil Environmental and Geo-Engineering University of Minnesota MN United States of America4 Division of Quantitative Sustainability Assessment Technical University of Denmark Denmark5 School for Environment and Sustainability University of Michigan MI United States of America6 Civil and Environmental Engineering University of Michigan MI United States of America7 Author to whom any correspondence should be addressed
OPEN ACCESS
RECEIVED
15 September 2016
REVISED
21 August 2017
ACCEPTED FOR PUBLICATION
25 August 2017
PUBLISHED
5 December 2017
Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 30 licenceAny further distributionof this work mustmaintain attribution tothe author(s) and thetitle of the work journalcitation and DOI
E-mail emoharebreadingacuk
Keywords urban agriculture energy food systems resource efficiency industrial ecology local food foodndashenergyndashwater nexus
AbstractThere is an increasing global interest in scaling up urban agriculture (UA) in its various forms fromprivate gardens to sophisticated commercial operations Much of this interest is in the spirit ofenvironmental protection with reduced waste and transportation energy highlighted as some of theproposed benefits of UA however explicit consideration of energy and resource requirements needsto be made in order to realize these anticipated environmental benefits A literature review isundertaken here to provide new insight into the energy implications of scaling up UA in cities inhigh-income countries considering UA classification directindirect energy pressures andinteractions with other components of the foodndashenergyndashwater nexus This is followed by anexploration of ways in which these cities can plan for the exploitation of waste flows forresource-efficient UA
Given that it is estimated that the food system contributes nearly 15 of total US energy demandoptimization of resource use in food production distribution consumption and waste systems mayhave a significant energy impact There are limited data available that quantify resource demandimplications directly associated with UA systems highlighting that the literature is not yet sufficientlyrobust to make universal claims on benefits This letter explores energy demand from conventionalresource inputs various production systems waterenergy trade-offs alternative irrigation packagingmaterials and transportationsupply chains to shed light on UA-focused research needs
By analyzing data and cases from the existing literature we propose that gains in energy efficiencycould be realized through the co-location of UA operations with waste streams (eg heat CO2greywater wastewater compost) potentially increasing yields and offsetting life cycle energydemands relative to conventional approaches This begs a number of energy-focused UA researchquestions that explore the opportunities for integrating the variety of UA structures and technologiesso that they are better able to exploit these urban waste flows and achieve whole-system reductions inenergy demand Any planning approach to implement these must as always assess how context willinfluence the viability and value added from the promotion of UA
Introduction
Urban agriculture (UA) has been undergoing a globalresurgence in recent decades with cities in bothadvanced and emerging economies implementing
programs to encourage its use (Mok et al 2013Orsini et al 2013 Hamilton et al 2013 Vitiello andBrinkley 2013) This renewed interest has led to theexploration of the extent to which UA could beexpanded including a number of investigations that
copy 2017 IOP Publishing Ltd
Environ Res Lett 12 (2017) 125004
estimate the potential for UA to meet local fooddemand for example Grewal and Grewal (2012)McClintock et al (2013) and Goldstein et al (2017)suggest provision of total food demand (former) andvegetable demand (latter two) of 42minus177 5and 32 respectively Expanding UA is expected toimprove local sustainability includingbenefits to social(addressing food deserts building community cohe-sion or higher intake of fresh produce) and economic(cash crop production reduced food costs) facets ofcities The environmental aspects associated with thenet direct and indirect energy implications of UA willbe the primary sustainability focus area of this research
Part of the rationale for reconsidering UA has beenits potential environmental benefits including reduc-tions in energy demand throughout the food supplychain As a result UA has been included in green-house gas (GHG) mitigation strategies for cities (Arupand C40 Cities 2014) and broader urban sustainabilityagendas through multi-city agreements and partner-ships suchas theUKrsquosSustainableFoodCitiesNetworkand the Milan Urban Food Policy Pact the latter ofwhich includes 100 large cities around the world (Milan2015 Andrews et al 2017) However when consider-ing the complex interplay between food productionenergy requirements and water availability (ie thefoodndashenergyndashwater nexus) the ability of UA to reduceenergy demand is unclear
This review article examines energy use in thefood system explores the opportunities that exist forhigh-income cities to increase the energyresourceefficiency of this overall system through UA andproposes changes that could be made in the plan-ning of cities to enable greater reductions in energydemand with a focus on the United States The scopeextends beyond the frequently-assessed topic of trans-portation into topics such as embodied energy ofproduction inputs (ie water nutrients heating CO2)reduction in packaging storage and processing needsThis review aims to provide a point of reference forenergy considerations that should be made if UA isgoing to provide a greater share of the global foodsupply
Classifying urban agriculture
Estimating the current scale of UA is difficult and variesbased on how it is defined for example Thebo et al(2014) estimate that there were 67 megahectares (Mha106 ha) of UA8 globally in 2000 (5 of global arableland in that year Food and Agriculture Organiza-tion 2010 table A4) with roughly 13 of the UA areabeing irrigated Their quantification includes spatial
8 Thebo et al (2014) define urban agriculture as the spatial coinci-dence of agricultural areas with urban extents with populations over50 000
data where agricultural areas and urban boundarieswith populations greater than 50 000 overlap most ofwhich would be classified as peri-urban9 agricultureand would not capture small-scale operations such asresidential gardens vacant lots or building-integratedproduction (eg balcony gardens rooftop gardens)Inclusion of peri-urban agriculture would produce asubstantially higher estimate of UA than the area thatis currently used in these more commonly-perceivedforms of UA Looking at the scale of some of thesetypes of UA Taylor and Lovell (2012) examine thetotal area of UA in the city of Chicago using 2010 aerialphotographs They find that approximately 004of Chicagorsquos land area of 606 km2 was being usedfor urban agriculture of this nearly half (45) wasin residential gardens while most of the remainderwas in vacant lots (27) and community food gardens(21) To provide a sense of scale of the opportunityto expand urban agriculture a 2000 study of vacantland in US cities finds that those in the Midwest had anaverage of 12 vacant land and a national average of15 (Pagano and Bowman 2000)10
As alluded to above UA manifests itself in a num-ber of different structures and locations within thebuilt environment Attempts have been made in theliterature to classify UA Mok et al (2013) identifythree distinct scales of agriculture in urban systemsThese are (in order of decreasing size) small com-mercial farms and community-supported agriculturecommunity gardens and backyard gardens All of theseUA scales differ in their structure inputs and pro-ductivity as a result their net impact on life cycleenergy demand and other resource inputs also variesGoldstein et al (2016b) further classify UA to con-sider structure and inputs in a taxonomic schemebased on the conditioning required for the growingenvironment (temperature light and CO2 control)and integration within the surrounding urban system(building integrated or ground based) They claim thatboth features are important to UA energy regimeswith space conditioning (particularly the need for heat-ing in cold climates) being an essential considerationalong with the potential for building integrated farmsto utilize dissipative heat and CO2 to offset productioninputs
A broad classification of UA is provided in table1 which is roughly ordered by scale and sophisti-cation of production It should be highlighted thatwhile the preservation of peri-urban agriculture canbe captured in assessments of UA the focus ofthis review is on approaches to scaling up UA that
9 Peri-urban agriculture refers to agricultural production that occursat the urbanndashrural interface10 Data include vacant land with and without abandoned buildingsChicago did not provide data for this study to allow a direct com-parison hence the average area for Midwest cities is provided hereas well it is not being suggested here that all vacant land be allocatedto or are suitable for UA
2
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
CentAUR
Central Archive at the University of Reading
Readingrsquos research outputs online
Environmental Research Letters
LETTER bull OPEN ACCESS
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LETTER
Considerations for reducing food system energy demandwhile scaling up urban agriculture
Eugene Mohareb17 Martin Heller2 Paige Novak3 Benjamin Goldstein45 Xavier Fonoll6 andLutgarde Raskin6
1 School of the Built Environment University of Reading Reading United Kingdom2 Center for Sustainable Systems University of Michigan MI United States of America3 Department of Civil Environmental and Geo-Engineering University of Minnesota MN United States of America4 Division of Quantitative Sustainability Assessment Technical University of Denmark Denmark5 School for Environment and Sustainability University of Michigan MI United States of America6 Civil and Environmental Engineering University of Michigan MI United States of America7 Author to whom any correspondence should be addressed
OPEN ACCESS
RECEIVED
15 September 2016
REVISED
21 August 2017
ACCEPTED FOR PUBLICATION
25 August 2017
PUBLISHED
5 December 2017
Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 30 licenceAny further distributionof this work mustmaintain attribution tothe author(s) and thetitle of the work journalcitation and DOI
E-mail emoharebreadingacuk
Keywords urban agriculture energy food systems resource efficiency industrial ecology local food foodndashenergyndashwater nexus
AbstractThere is an increasing global interest in scaling up urban agriculture (UA) in its various forms fromprivate gardens to sophisticated commercial operations Much of this interest is in the spirit ofenvironmental protection with reduced waste and transportation energy highlighted as some of theproposed benefits of UA however explicit consideration of energy and resource requirements needsto be made in order to realize these anticipated environmental benefits A literature review isundertaken here to provide new insight into the energy implications of scaling up UA in cities inhigh-income countries considering UA classification directindirect energy pressures andinteractions with other components of the foodndashenergyndashwater nexus This is followed by anexploration of ways in which these cities can plan for the exploitation of waste flows forresource-efficient UA
Given that it is estimated that the food system contributes nearly 15 of total US energy demandoptimization of resource use in food production distribution consumption and waste systems mayhave a significant energy impact There are limited data available that quantify resource demandimplications directly associated with UA systems highlighting that the literature is not yet sufficientlyrobust to make universal claims on benefits This letter explores energy demand from conventionalresource inputs various production systems waterenergy trade-offs alternative irrigation packagingmaterials and transportationsupply chains to shed light on UA-focused research needs
By analyzing data and cases from the existing literature we propose that gains in energy efficiencycould be realized through the co-location of UA operations with waste streams (eg heat CO2greywater wastewater compost) potentially increasing yields and offsetting life cycle energydemands relative to conventional approaches This begs a number of energy-focused UA researchquestions that explore the opportunities for integrating the variety of UA structures and technologiesso that they are better able to exploit these urban waste flows and achieve whole-system reductions inenergy demand Any planning approach to implement these must as always assess how context willinfluence the viability and value added from the promotion of UA
Introduction
Urban agriculture (UA) has been undergoing a globalresurgence in recent decades with cities in bothadvanced and emerging economies implementing
programs to encourage its use (Mok et al 2013Orsini et al 2013 Hamilton et al 2013 Vitiello andBrinkley 2013) This renewed interest has led to theexploration of the extent to which UA could beexpanded including a number of investigations that
copy 2017 IOP Publishing Ltd
Environ Res Lett 12 (2017) 125004
estimate the potential for UA to meet local fooddemand for example Grewal and Grewal (2012)McClintock et al (2013) and Goldstein et al (2017)suggest provision of total food demand (former) andvegetable demand (latter two) of 42minus177 5and 32 respectively Expanding UA is expected toimprove local sustainability includingbenefits to social(addressing food deserts building community cohe-sion or higher intake of fresh produce) and economic(cash crop production reduced food costs) facets ofcities The environmental aspects associated with thenet direct and indirect energy implications of UA willbe the primary sustainability focus area of this research
Part of the rationale for reconsidering UA has beenits potential environmental benefits including reduc-tions in energy demand throughout the food supplychain As a result UA has been included in green-house gas (GHG) mitigation strategies for cities (Arupand C40 Cities 2014) and broader urban sustainabilityagendas through multi-city agreements and partner-ships suchas theUKrsquosSustainableFoodCitiesNetworkand the Milan Urban Food Policy Pact the latter ofwhich includes 100 large cities around the world (Milan2015 Andrews et al 2017) However when consider-ing the complex interplay between food productionenergy requirements and water availability (ie thefoodndashenergyndashwater nexus) the ability of UA to reduceenergy demand is unclear
This review article examines energy use in thefood system explores the opportunities that exist forhigh-income cities to increase the energyresourceefficiency of this overall system through UA andproposes changes that could be made in the plan-ning of cities to enable greater reductions in energydemand with a focus on the United States The scopeextends beyond the frequently-assessed topic of trans-portation into topics such as embodied energy ofproduction inputs (ie water nutrients heating CO2)reduction in packaging storage and processing needsThis review aims to provide a point of reference forenergy considerations that should be made if UA isgoing to provide a greater share of the global foodsupply
Classifying urban agriculture
Estimating the current scale of UA is difficult and variesbased on how it is defined for example Thebo et al(2014) estimate that there were 67 megahectares (Mha106 ha) of UA8 globally in 2000 (5 of global arableland in that year Food and Agriculture Organiza-tion 2010 table A4) with roughly 13 of the UA areabeing irrigated Their quantification includes spatial
8 Thebo et al (2014) define urban agriculture as the spatial coinci-dence of agricultural areas with urban extents with populations over50 000
data where agricultural areas and urban boundarieswith populations greater than 50 000 overlap most ofwhich would be classified as peri-urban9 agricultureand would not capture small-scale operations such asresidential gardens vacant lots or building-integratedproduction (eg balcony gardens rooftop gardens)Inclusion of peri-urban agriculture would produce asubstantially higher estimate of UA than the area thatis currently used in these more commonly-perceivedforms of UA Looking at the scale of some of thesetypes of UA Taylor and Lovell (2012) examine thetotal area of UA in the city of Chicago using 2010 aerialphotographs They find that approximately 004of Chicagorsquos land area of 606 km2 was being usedfor urban agriculture of this nearly half (45) wasin residential gardens while most of the remainderwas in vacant lots (27) and community food gardens(21) To provide a sense of scale of the opportunityto expand urban agriculture a 2000 study of vacantland in US cities finds that those in the Midwest had anaverage of 12 vacant land and a national average of15 (Pagano and Bowman 2000)10
As alluded to above UA manifests itself in a num-ber of different structures and locations within thebuilt environment Attempts have been made in theliterature to classify UA Mok et al (2013) identifythree distinct scales of agriculture in urban systemsThese are (in order of decreasing size) small com-mercial farms and community-supported agriculturecommunity gardens and backyard gardens All of theseUA scales differ in their structure inputs and pro-ductivity as a result their net impact on life cycleenergy demand and other resource inputs also variesGoldstein et al (2016b) further classify UA to con-sider structure and inputs in a taxonomic schemebased on the conditioning required for the growingenvironment (temperature light and CO2 control)and integration within the surrounding urban system(building integrated or ground based) They claim thatboth features are important to UA energy regimeswith space conditioning (particularly the need for heat-ing in cold climates) being an essential considerationalong with the potential for building integrated farmsto utilize dissipative heat and CO2 to offset productioninputs
A broad classification of UA is provided in table1 which is roughly ordered by scale and sophisti-cation of production It should be highlighted thatwhile the preservation of peri-urban agriculture canbe captured in assessments of UA the focus ofthis review is on approaches to scaling up UA that
9 Peri-urban agriculture refers to agricultural production that occursat the urbanndashrural interface10 Data include vacant land with and without abandoned buildingsChicago did not provide data for this study to allow a direct com-parison hence the average area for Midwest cities is provided hereas well it is not being suggested here that all vacant land be allocatedto or are suitable for UA
2
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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16
Environmental Research Letters
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Considerations for reducing food system energy demand while scalingup urban agricultureTo cite this article Eugene Mohareb et al 2017 Environ Res Lett 12 125004
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LETTER
Considerations for reducing food system energy demandwhile scaling up urban agriculture
Eugene Mohareb17 Martin Heller2 Paige Novak3 Benjamin Goldstein45 Xavier Fonoll6 andLutgarde Raskin6
1 School of the Built Environment University of Reading Reading United Kingdom2 Center for Sustainable Systems University of Michigan MI United States of America3 Department of Civil Environmental and Geo-Engineering University of Minnesota MN United States of America4 Division of Quantitative Sustainability Assessment Technical University of Denmark Denmark5 School for Environment and Sustainability University of Michigan MI United States of America6 Civil and Environmental Engineering University of Michigan MI United States of America7 Author to whom any correspondence should be addressed
OPEN ACCESS
RECEIVED
15 September 2016
REVISED
21 August 2017
ACCEPTED FOR PUBLICATION
25 August 2017
PUBLISHED
5 December 2017
Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 30 licenceAny further distributionof this work mustmaintain attribution tothe author(s) and thetitle of the work journalcitation and DOI
E-mail emoharebreadingacuk
Keywords urban agriculture energy food systems resource efficiency industrial ecology local food foodndashenergyndashwater nexus
AbstractThere is an increasing global interest in scaling up urban agriculture (UA) in its various forms fromprivate gardens to sophisticated commercial operations Much of this interest is in the spirit ofenvironmental protection with reduced waste and transportation energy highlighted as some of theproposed benefits of UA however explicit consideration of energy and resource requirements needsto be made in order to realize these anticipated environmental benefits A literature review isundertaken here to provide new insight into the energy implications of scaling up UA in cities inhigh-income countries considering UA classification directindirect energy pressures andinteractions with other components of the foodndashenergyndashwater nexus This is followed by anexploration of ways in which these cities can plan for the exploitation of waste flows forresource-efficient UA
Given that it is estimated that the food system contributes nearly 15 of total US energy demandoptimization of resource use in food production distribution consumption and waste systems mayhave a significant energy impact There are limited data available that quantify resource demandimplications directly associated with UA systems highlighting that the literature is not yet sufficientlyrobust to make universal claims on benefits This letter explores energy demand from conventionalresource inputs various production systems waterenergy trade-offs alternative irrigation packagingmaterials and transportationsupply chains to shed light on UA-focused research needs
By analyzing data and cases from the existing literature we propose that gains in energy efficiencycould be realized through the co-location of UA operations with waste streams (eg heat CO2greywater wastewater compost) potentially increasing yields and offsetting life cycle energydemands relative to conventional approaches This begs a number of energy-focused UA researchquestions that explore the opportunities for integrating the variety of UA structures and technologiesso that they are better able to exploit these urban waste flows and achieve whole-system reductions inenergy demand Any planning approach to implement these must as always assess how context willinfluence the viability and value added from the promotion of UA
Introduction
Urban agriculture (UA) has been undergoing a globalresurgence in recent decades with cities in bothadvanced and emerging economies implementing
programs to encourage its use (Mok et al 2013Orsini et al 2013 Hamilton et al 2013 Vitiello andBrinkley 2013) This renewed interest has led to theexploration of the extent to which UA could beexpanded including a number of investigations that
copy 2017 IOP Publishing Ltd
Environ Res Lett 12 (2017) 125004
estimate the potential for UA to meet local fooddemand for example Grewal and Grewal (2012)McClintock et al (2013) and Goldstein et al (2017)suggest provision of total food demand (former) andvegetable demand (latter two) of 42minus177 5and 32 respectively Expanding UA is expected toimprove local sustainability includingbenefits to social(addressing food deserts building community cohe-sion or higher intake of fresh produce) and economic(cash crop production reduced food costs) facets ofcities The environmental aspects associated with thenet direct and indirect energy implications of UA willbe the primary sustainability focus area of this research
Part of the rationale for reconsidering UA has beenits potential environmental benefits including reduc-tions in energy demand throughout the food supplychain As a result UA has been included in green-house gas (GHG) mitigation strategies for cities (Arupand C40 Cities 2014) and broader urban sustainabilityagendas through multi-city agreements and partner-ships suchas theUKrsquosSustainableFoodCitiesNetworkand the Milan Urban Food Policy Pact the latter ofwhich includes 100 large cities around the world (Milan2015 Andrews et al 2017) However when consider-ing the complex interplay between food productionenergy requirements and water availability (ie thefoodndashenergyndashwater nexus) the ability of UA to reduceenergy demand is unclear
This review article examines energy use in thefood system explores the opportunities that exist forhigh-income cities to increase the energyresourceefficiency of this overall system through UA andproposes changes that could be made in the plan-ning of cities to enable greater reductions in energydemand with a focus on the United States The scopeextends beyond the frequently-assessed topic of trans-portation into topics such as embodied energy ofproduction inputs (ie water nutrients heating CO2)reduction in packaging storage and processing needsThis review aims to provide a point of reference forenergy considerations that should be made if UA isgoing to provide a greater share of the global foodsupply
Classifying urban agriculture
Estimating the current scale of UA is difficult and variesbased on how it is defined for example Thebo et al(2014) estimate that there were 67 megahectares (Mha106 ha) of UA8 globally in 2000 (5 of global arableland in that year Food and Agriculture Organiza-tion 2010 table A4) with roughly 13 of the UA areabeing irrigated Their quantification includes spatial
8 Thebo et al (2014) define urban agriculture as the spatial coinci-dence of agricultural areas with urban extents with populations over50 000
data where agricultural areas and urban boundarieswith populations greater than 50 000 overlap most ofwhich would be classified as peri-urban9 agricultureand would not capture small-scale operations such asresidential gardens vacant lots or building-integratedproduction (eg balcony gardens rooftop gardens)Inclusion of peri-urban agriculture would produce asubstantially higher estimate of UA than the area thatis currently used in these more commonly-perceivedforms of UA Looking at the scale of some of thesetypes of UA Taylor and Lovell (2012) examine thetotal area of UA in the city of Chicago using 2010 aerialphotographs They find that approximately 004of Chicagorsquos land area of 606 km2 was being usedfor urban agriculture of this nearly half (45) wasin residential gardens while most of the remainderwas in vacant lots (27) and community food gardens(21) To provide a sense of scale of the opportunityto expand urban agriculture a 2000 study of vacantland in US cities finds that those in the Midwest had anaverage of 12 vacant land and a national average of15 (Pagano and Bowman 2000)10
As alluded to above UA manifests itself in a num-ber of different structures and locations within thebuilt environment Attempts have been made in theliterature to classify UA Mok et al (2013) identifythree distinct scales of agriculture in urban systemsThese are (in order of decreasing size) small com-mercial farms and community-supported agriculturecommunity gardens and backyard gardens All of theseUA scales differ in their structure inputs and pro-ductivity as a result their net impact on life cycleenergy demand and other resource inputs also variesGoldstein et al (2016b) further classify UA to con-sider structure and inputs in a taxonomic schemebased on the conditioning required for the growingenvironment (temperature light and CO2 control)and integration within the surrounding urban system(building integrated or ground based) They claim thatboth features are important to UA energy regimeswith space conditioning (particularly the need for heat-ing in cold climates) being an essential considerationalong with the potential for building integrated farmsto utilize dissipative heat and CO2 to offset productioninputs
A broad classification of UA is provided in table1 which is roughly ordered by scale and sophisti-cation of production It should be highlighted thatwhile the preservation of peri-urban agriculture canbe captured in assessments of UA the focus ofthis review is on approaches to scaling up UA that
9 Peri-urban agriculture refers to agricultural production that occursat the urbanndashrural interface10 Data include vacant land with and without abandoned buildingsChicago did not provide data for this study to allow a direct com-parison hence the average area for Midwest cities is provided hereas well it is not being suggested here that all vacant land be allocatedto or are suitable for UA
2
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004 httpsdoiorg1010881748-9326aa889b
LETTER
Considerations for reducing food system energy demandwhile scaling up urban agriculture
Eugene Mohareb17 Martin Heller2 Paige Novak3 Benjamin Goldstein45 Xavier Fonoll6 andLutgarde Raskin6
1 School of the Built Environment University of Reading Reading United Kingdom2 Center for Sustainable Systems University of Michigan MI United States of America3 Department of Civil Environmental and Geo-Engineering University of Minnesota MN United States of America4 Division of Quantitative Sustainability Assessment Technical University of Denmark Denmark5 School for Environment and Sustainability University of Michigan MI United States of America6 Civil and Environmental Engineering University of Michigan MI United States of America7 Author to whom any correspondence should be addressed
OPEN ACCESS
RECEIVED
15 September 2016
REVISED
21 August 2017
ACCEPTED FOR PUBLICATION
25 August 2017
PUBLISHED
5 December 2017
Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 30 licenceAny further distributionof this work mustmaintain attribution tothe author(s) and thetitle of the work journalcitation and DOI
E-mail emoharebreadingacuk
Keywords urban agriculture energy food systems resource efficiency industrial ecology local food foodndashenergyndashwater nexus
AbstractThere is an increasing global interest in scaling up urban agriculture (UA) in its various forms fromprivate gardens to sophisticated commercial operations Much of this interest is in the spirit ofenvironmental protection with reduced waste and transportation energy highlighted as some of theproposed benefits of UA however explicit consideration of energy and resource requirements needsto be made in order to realize these anticipated environmental benefits A literature review isundertaken here to provide new insight into the energy implications of scaling up UA in cities inhigh-income countries considering UA classification directindirect energy pressures andinteractions with other components of the foodndashenergyndashwater nexus This is followed by anexploration of ways in which these cities can plan for the exploitation of waste flows forresource-efficient UA
Given that it is estimated that the food system contributes nearly 15 of total US energy demandoptimization of resource use in food production distribution consumption and waste systems mayhave a significant energy impact There are limited data available that quantify resource demandimplications directly associated with UA systems highlighting that the literature is not yet sufficientlyrobust to make universal claims on benefits This letter explores energy demand from conventionalresource inputs various production systems waterenergy trade-offs alternative irrigation packagingmaterials and transportationsupply chains to shed light on UA-focused research needs
By analyzing data and cases from the existing literature we propose that gains in energy efficiencycould be realized through the co-location of UA operations with waste streams (eg heat CO2greywater wastewater compost) potentially increasing yields and offsetting life cycle energydemands relative to conventional approaches This begs a number of energy-focused UA researchquestions that explore the opportunities for integrating the variety of UA structures and technologiesso that they are better able to exploit these urban waste flows and achieve whole-system reductions inenergy demand Any planning approach to implement these must as always assess how context willinfluence the viability and value added from the promotion of UA
Introduction
Urban agriculture (UA) has been undergoing a globalresurgence in recent decades with cities in bothadvanced and emerging economies implementing
programs to encourage its use (Mok et al 2013Orsini et al 2013 Hamilton et al 2013 Vitiello andBrinkley 2013) This renewed interest has led to theexploration of the extent to which UA could beexpanded including a number of investigations that
copy 2017 IOP Publishing Ltd
Environ Res Lett 12 (2017) 125004
estimate the potential for UA to meet local fooddemand for example Grewal and Grewal (2012)McClintock et al (2013) and Goldstein et al (2017)suggest provision of total food demand (former) andvegetable demand (latter two) of 42minus177 5and 32 respectively Expanding UA is expected toimprove local sustainability includingbenefits to social(addressing food deserts building community cohe-sion or higher intake of fresh produce) and economic(cash crop production reduced food costs) facets ofcities The environmental aspects associated with thenet direct and indirect energy implications of UA willbe the primary sustainability focus area of this research
Part of the rationale for reconsidering UA has beenits potential environmental benefits including reduc-tions in energy demand throughout the food supplychain As a result UA has been included in green-house gas (GHG) mitigation strategies for cities (Arupand C40 Cities 2014) and broader urban sustainabilityagendas through multi-city agreements and partner-ships suchas theUKrsquosSustainableFoodCitiesNetworkand the Milan Urban Food Policy Pact the latter ofwhich includes 100 large cities around the world (Milan2015 Andrews et al 2017) However when consider-ing the complex interplay between food productionenergy requirements and water availability (ie thefoodndashenergyndashwater nexus) the ability of UA to reduceenergy demand is unclear
This review article examines energy use in thefood system explores the opportunities that exist forhigh-income cities to increase the energyresourceefficiency of this overall system through UA andproposes changes that could be made in the plan-ning of cities to enable greater reductions in energydemand with a focus on the United States The scopeextends beyond the frequently-assessed topic of trans-portation into topics such as embodied energy ofproduction inputs (ie water nutrients heating CO2)reduction in packaging storage and processing needsThis review aims to provide a point of reference forenergy considerations that should be made if UA isgoing to provide a greater share of the global foodsupply
Classifying urban agriculture
Estimating the current scale of UA is difficult and variesbased on how it is defined for example Thebo et al(2014) estimate that there were 67 megahectares (Mha106 ha) of UA8 globally in 2000 (5 of global arableland in that year Food and Agriculture Organiza-tion 2010 table A4) with roughly 13 of the UA areabeing irrigated Their quantification includes spatial
8 Thebo et al (2014) define urban agriculture as the spatial coinci-dence of agricultural areas with urban extents with populations over50 000
data where agricultural areas and urban boundarieswith populations greater than 50 000 overlap most ofwhich would be classified as peri-urban9 agricultureand would not capture small-scale operations such asresidential gardens vacant lots or building-integratedproduction (eg balcony gardens rooftop gardens)Inclusion of peri-urban agriculture would produce asubstantially higher estimate of UA than the area thatis currently used in these more commonly-perceivedforms of UA Looking at the scale of some of thesetypes of UA Taylor and Lovell (2012) examine thetotal area of UA in the city of Chicago using 2010 aerialphotographs They find that approximately 004of Chicagorsquos land area of 606 km2 was being usedfor urban agriculture of this nearly half (45) wasin residential gardens while most of the remainderwas in vacant lots (27) and community food gardens(21) To provide a sense of scale of the opportunityto expand urban agriculture a 2000 study of vacantland in US cities finds that those in the Midwest had anaverage of 12 vacant land and a national average of15 (Pagano and Bowman 2000)10
As alluded to above UA manifests itself in a num-ber of different structures and locations within thebuilt environment Attempts have been made in theliterature to classify UA Mok et al (2013) identifythree distinct scales of agriculture in urban systemsThese are (in order of decreasing size) small com-mercial farms and community-supported agriculturecommunity gardens and backyard gardens All of theseUA scales differ in their structure inputs and pro-ductivity as a result their net impact on life cycleenergy demand and other resource inputs also variesGoldstein et al (2016b) further classify UA to con-sider structure and inputs in a taxonomic schemebased on the conditioning required for the growingenvironment (temperature light and CO2 control)and integration within the surrounding urban system(building integrated or ground based) They claim thatboth features are important to UA energy regimeswith space conditioning (particularly the need for heat-ing in cold climates) being an essential considerationalong with the potential for building integrated farmsto utilize dissipative heat and CO2 to offset productioninputs
A broad classification of UA is provided in table1 which is roughly ordered by scale and sophisti-cation of production It should be highlighted thatwhile the preservation of peri-urban agriculture canbe captured in assessments of UA the focus ofthis review is on approaches to scaling up UA that
9 Peri-urban agriculture refers to agricultural production that occursat the urbanndashrural interface10 Data include vacant land with and without abandoned buildingsChicago did not provide data for this study to allow a direct com-parison hence the average area for Midwest cities is provided hereas well it is not being suggested here that all vacant land be allocatedto or are suitable for UA
2
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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16
Environ Res Lett 12 (2017) 125004
estimate the potential for UA to meet local fooddemand for example Grewal and Grewal (2012)McClintock et al (2013) and Goldstein et al (2017)suggest provision of total food demand (former) andvegetable demand (latter two) of 42minus177 5and 32 respectively Expanding UA is expected toimprove local sustainability includingbenefits to social(addressing food deserts building community cohe-sion or higher intake of fresh produce) and economic(cash crop production reduced food costs) facets ofcities The environmental aspects associated with thenet direct and indirect energy implications of UA willbe the primary sustainability focus area of this research
Part of the rationale for reconsidering UA has beenits potential environmental benefits including reduc-tions in energy demand throughout the food supplychain As a result UA has been included in green-house gas (GHG) mitigation strategies for cities (Arupand C40 Cities 2014) and broader urban sustainabilityagendas through multi-city agreements and partner-ships suchas theUKrsquosSustainableFoodCitiesNetworkand the Milan Urban Food Policy Pact the latter ofwhich includes 100 large cities around the world (Milan2015 Andrews et al 2017) However when consider-ing the complex interplay between food productionenergy requirements and water availability (ie thefoodndashenergyndashwater nexus) the ability of UA to reduceenergy demand is unclear
This review article examines energy use in thefood system explores the opportunities that exist forhigh-income cities to increase the energyresourceefficiency of this overall system through UA andproposes changes that could be made in the plan-ning of cities to enable greater reductions in energydemand with a focus on the United States The scopeextends beyond the frequently-assessed topic of trans-portation into topics such as embodied energy ofproduction inputs (ie water nutrients heating CO2)reduction in packaging storage and processing needsThis review aims to provide a point of reference forenergy considerations that should be made if UA isgoing to provide a greater share of the global foodsupply
Classifying urban agriculture
Estimating the current scale of UA is difficult and variesbased on how it is defined for example Thebo et al(2014) estimate that there were 67 megahectares (Mha106 ha) of UA8 globally in 2000 (5 of global arableland in that year Food and Agriculture Organiza-tion 2010 table A4) with roughly 13 of the UA areabeing irrigated Their quantification includes spatial
8 Thebo et al (2014) define urban agriculture as the spatial coinci-dence of agricultural areas with urban extents with populations over50 000
data where agricultural areas and urban boundarieswith populations greater than 50 000 overlap most ofwhich would be classified as peri-urban9 agricultureand would not capture small-scale operations such asresidential gardens vacant lots or building-integratedproduction (eg balcony gardens rooftop gardens)Inclusion of peri-urban agriculture would produce asubstantially higher estimate of UA than the area thatis currently used in these more commonly-perceivedforms of UA Looking at the scale of some of thesetypes of UA Taylor and Lovell (2012) examine thetotal area of UA in the city of Chicago using 2010 aerialphotographs They find that approximately 004of Chicagorsquos land area of 606 km2 was being usedfor urban agriculture of this nearly half (45) wasin residential gardens while most of the remainderwas in vacant lots (27) and community food gardens(21) To provide a sense of scale of the opportunityto expand urban agriculture a 2000 study of vacantland in US cities finds that those in the Midwest had anaverage of 12 vacant land and a national average of15 (Pagano and Bowman 2000)10
As alluded to above UA manifests itself in a num-ber of different structures and locations within thebuilt environment Attempts have been made in theliterature to classify UA Mok et al (2013) identifythree distinct scales of agriculture in urban systemsThese are (in order of decreasing size) small com-mercial farms and community-supported agriculturecommunity gardens and backyard gardens All of theseUA scales differ in their structure inputs and pro-ductivity as a result their net impact on life cycleenergy demand and other resource inputs also variesGoldstein et al (2016b) further classify UA to con-sider structure and inputs in a taxonomic schemebased on the conditioning required for the growingenvironment (temperature light and CO2 control)and integration within the surrounding urban system(building integrated or ground based) They claim thatboth features are important to UA energy regimeswith space conditioning (particularly the need for heat-ing in cold climates) being an essential considerationalong with the potential for building integrated farmsto utilize dissipative heat and CO2 to offset productioninputs
A broad classification of UA is provided in table1 which is roughly ordered by scale and sophisti-cation of production It should be highlighted thatwhile the preservation of peri-urban agriculture canbe captured in assessments of UA the focus ofthis review is on approaches to scaling up UA that
9 Peri-urban agriculture refers to agricultural production that occursat the urbanndashrural interface10 Data include vacant land with and without abandoned buildingsChicago did not provide data for this study to allow a direct com-parison hence the average area for Midwest cities is provided hereas well it is not being suggested here that all vacant land be allocatedto or are suitable for UA
2
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
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Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
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IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
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Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Table 1 Type of urban agriculture associated with structurelocation of production potential beneficial energy impacts relative to intensiverural agriculture and requirements for upscaling
Type of urban
agricultureAuthorsrsquo definition Potential direct energy
benefitsConsiderations for successful
upscalingSources
Residentialgardens
Open air or protected11 food
production occurring within
the boundaries of a residential
property primarily for
personal consumption
∙ Non-mechanized
inputs
∙Reduced cold
chainretail
requirement (onsite
end-consumption)
∙ Knowledge dissemination
for production preservation
∙ Regulations for application
of fertilizers pesticides
∙ Appropriate crop selection
(Kulak et al 2013
Altieri et al 1999)
Allotment andcommunitygardens12
Open air or protected food
production occurring upon
community or municipally-
owned land primarily for
personal consumption
∙ Non-mechanized
inputs
∙ Reduced cold
chainretail
requirement
∙ Municipal allocation of
green space
∙ Expedited application
approval to facilitate utility
connection
∙ Mulch from municipal
greenspace maintenance
(Leach 1975)
Rooftopbalconyagriculture
Open air or protected food
production occurring on
structures built for other
primary functions for either
personal consumption or
commercial availability
∙ Thermal transfer
from rooftop
∙ Improved yield
∙ Improved building
insulation
∙ Onsite waste
diversion
∙ Building code consideration
(structural utilities)
(Sanye-Mengual et al
2015 Saiz et al 2006
Specht et al 2013
Grard et al 2015
Orsini et al 2014)
Industryresidence-integratedgreenhouse
Controlled-environment food
production with supplemental
heating integrated into
structures built for other
primary functions that involve
purpose-built infrastructure
for yield improvement
towards commercial
availability
∙ Waste heatCO2utilization
∙ Improved yield
∙ Inventory of urban resource
streams
∙ Zoning by-laws to enable
co-location of agriculture with
resources
(Zhang et al 2013)
Vertical farms Controlled-environment food
production with supplemental
heating in multi-story
structures developed with the
primary function of crop
production for commercial
availability Generally located
within urban boundaries
∙ Onsite waste
diversion (eg
waste-to-feed for
livestock operations)
∙ Potential for on-site
nutrient cycling
∙ Improved yield
∙ Building code changes
(structural utilities)
∙ Innovations in lighting
agriculture system integration
in built environment
∙ Low-carbon grid due to
expected substantial energy
requirements
(Despommier 2013
Hamm 2015)
Peri-urbanagriculture
Open air protected or
supplemental heat
environment food production
at the urban-rural interface
Generally for commercial
availability but may include
subsistence agriculture in
developing-world contexts
∙ Preservation of
high-yielding prime
agricultural land
∙ Legal protection of
peripheral farmlands from
incompatible urban
development
(Francis et al 2012
Krannich 2006)
are integrated into the built environment ratherthan on maintaining existing agricultural land in theurban periphery Hence large scale conventional peri-urban agriculture is beyond the scope of inquiryhere
11 Protected food production refers to enclosed environments(eg with polyethylene or glass) that are not climate-controlledcontrolled-environment food production includes both protectedenvironments and those with supplemental heat12 Urban or peri-urban agricultural space designated and protectedby municipalities or community groups for non-commercial pur-poses
Energy consumption in the food system andurban agriculture
The modern food system encompasses a broad collec-tion of energy end-users Starting from the agriculturalphase through transportation of food to retailers andhouseholds and culminating in waste handling thecurrent predominantly linear structure of the foodsystem is highly dependent on energy inputs for itsoperations of production processing distributionconsumption and disposal of food products (Pimentelet al 2008) Examining the US case the USDA ERS
3
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Environ Res Lett 12 (2017) 125004
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Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Agriculture13
Processing17
Packaging5
Transportation3Wholesale Retail
15
Food Services18
Households29
Total = 14760 PJ
Figure 1 Energy consumption in the US food system in 2002 (adapted from Pelletier et al 2011 from Canning et al 2010)
Table 2 Energy and water demand per unit yielded for various tomato production systems (modified from Goldstein et al 2016a)
Production system Irrigation water (m Mgminus3) Direct and indirect energy demand (MJ Mgminus1)
Ground-based non-conditioned (two cases) 50 74 6500 2600Ground-based conditioned 65 33 000Building-integrated non-conditioned 68 3300Building-integrated conditioned 9 56 000Conventional (conditioned) 2 10 000
(2010) estimates that nearly 144 of total nationalenergy consumption in2002was food-relatedAbreak-down of this consumption is provided in figure 1
The majority of energy use in the food systemoccurs beyond the farm gate the United NationsFood and Agriculture Organization (FAO) estimatesthat over 75 of energy use in the food system ofhigh-income nations occurs after cultivation (Foodand Agriculture Organization 2013) This is consistentwith the 2002 US analysis in figure 1 which sug-gests that the post-agricultural energy use share is over87 However the potential for UA to impact energydemand beyond production is substantial (eg packag-ing processing transportation waste management) asdiscussed below In addition figure 1 excludes wastew-ater and food waste treatment therefore a completeconsideration of energy use associated with the expan-sion of UA will require an examination of not onlyfood productionbut also energy inputs across the entirefood system including waste handling and treatmentChanges in energy use relative to the status quo mustalso investigate the foodndashenergyndashwater nexus to vali-date theenvironmental case for scalingupUAandavoidany unintended shift of impacts from one resourcesystem (ie energy) to another (ie water)
Energy benefits of urban agricultureProponents suggest a number of energy-related ben-efits are realized through the reintroduction of foodproduction within cities (Howe and Wheeler 1999Garnett 1997 Smit and Nasr 1992 Kulak et al2013) Studies most commonly highlight savings intransportation energy reduced storage requirements
at the wholesaleresale level and energy inputs of foodwasteloss along the supply chain but also includeadditional biomass provision from silviculture (ieto offset energy imports Smit and Nasr 1992) eas-ier exploitation of resource use (Zhang et al 2013)and lower resource-intensity of production (Kulaket al 2013) Meanwhile peri-urban agriculturecan preserve higher-yielding prime agricultural land(Krannich 2006 Francis et al 2012) which has thepotential toprovide less resource-intensiveproductionLooking at more sophisticated integrated operations(vertical farms integrated greenhouses) exploitedwaste streams (CO2 heat macronutrients) could off-set energy requirements that are required for providingthese inputs in conventional operations (Despommier2013 Zhang et al 2013) Additionally if the distributednature of UA can be supported by a similarly dis-tributed energy infrastructure system foodagriculturewaste can be digested locally to generate biogas for heator electricity production further decreasing the energyfootprintofUAEnergy-relatedbenefitsassociatedwiththe various structureslocations of UA have also beendescribed in table 1 (excluding transportation)
Interactions with other components of theurban foodndashenergyndashwater nexus
Urban agriculture has the potential to affect energy-related components of the foodndashenergyndashwater systemwithin urban boundaries and beyond Suggestionsof positive and negative impacts both within andbeyond the urban boundary are presented in table 2
4
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
References
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Almeida J Achten W M J Verbist B Heuts R F Schrevens E andMuys B 2014 Carbon and water footprints and energy use ofgreenhouse tomato production in Northern Italy J Ind Ecol18 898ndash908
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Altieri M A Companioni N Canizares K Murphy C Rosset PBourque M and Nicholls C I 1999 The greening of thelsquobarriosrsquo urban agriculture for food security in Cuba AgricHuman Values 16 131ndash40
Amoah P Drechsel P Abaidoo R C and Henseler M 2007 Irrigatedurban vegetable production in Ghana microbiologicalcontamination in farms and markets and associated consumerrisk groups J Water Health 5 455ndash66
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13
Environ Res Lett 12 (2017) 125004
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Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
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Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
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Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
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Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
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Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
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Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
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Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
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Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
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Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
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Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
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16
Environ Res Lett 12 (2017) 125004
It is important to note that energy demand for ser-vices required in UA can differ from those providedthrough open-field agriculture An exploration of lit-erature that can provide greater insight on how thesedifferent UA approaches can influence energy needsfollows
Energy demand for UA water systemsEnergy demand in irrigation systems are a noteworthycomponent of scaled-up UA that must be consid-ered in order to avoid inadvertently increasing demandrelative to conventional open-field systems Irrigationsystems in an open-field agricultural setting are rela-tively low-energy when compared with potable urbanwater systems that could be used in UA in one studyopen-field irrigationenergydemand is estimatedat 063MJ mminus3 water (Esengun et al 2007 used in the absenceof a similar US case study) However in a UA systempotable water may be used for irrigation and generallyrequires substantially more energy for treatment withthe Electric Power Research Institute (2002) suggestingan estimate of 13 MJ mminus3 and 17 MJ mminus3 for pub-lic utilities using surface and groundwater respectively(including distribution) for a hypothetical 10 milliongallon per day treatment plant Meanwhile Racov-iceanu et al (2007) estimate energy demand at 23minus25MJ mminus3 treated water used in the City of Torontorsquoswater treatment The Racoviceanu et al (2007) studyconsiders a surface water source and includes chem-ical fabricationtransportation treatment and onsitepumping though most of total energy intensity(sim70) is attributable to untreated and treated waterpumping Data onMassachusettsrsquo 2007 energy demandfor water treatment and distribution suggests an aver-age value of 14 MJ mminus3 (US Environmental ProtectionAgency 2008) whereas Californiarsquos 2005 report onthe energy-water relationship provides estimates of 14MJ mminus3 and 97 MJ mminus3 for Northern and SouthernCalifornia respectively (range attributable to differ-ences in energy required for conveyance from sourceto treatment facilities Klein et al 2005) This latterCalifornia report also suggests that when desalinationoptions are employed in water treatment an additional93minus157 MJ mminus3 and 37minus93 MJ mminus3 are requiredfor seawater and brackish groundwater respectivelyIt is worth noting that depth of groundwater sourcepumping requirements for surfacegroundwater andon-farm treatment will influence the energy demandand could bring this figure closer in line with that fromwater utilities
The types of secondary energy used can also varyfor different types of irrigation influencing both costoverall energy efficiency and GHG emissions Forexample Ontario Canadarsquos field crop irrigation is typ-ically powered by diesel systems while greenhouseirrigation is generally powered by electricity (Carol2010) Diesel has an emissions intensity of 74 kgCO2e GJminus1 while electricity grid GHG intensity in
Ontario was 14 kg CO2e GJminus1 in 2014 (IPCC 2006chapter 3) For comparison US electricity emissionsintensities ranged from 1 to 266 kg CO2e GJminus1 in 2012(US EPA 2015)
Waterenergy trade-offs for UA production methodsWater use can be mitigated through the use of morewater-efficient growing systems (such as hydroponicsystems) though these can result in increased energydemand in pumping and lighting and associated GHGemissions For example hydroponic13 systems havebeen shown to have lower water demand than soil-based production in addition to avoiding the needfor a solid growing medium and the associated energyinputs of its provision (Albaho et al 2008) HoweverBarbosa et al (2015) have modeled energy and waterdemand for hydroponic and conventional productionsystems for lettuce while water demand was reduced by92 (250 to 20 l kgminus1 yminus1) energy demand increasedby 8100 (1100 to 90 000 kJ kgminus1 yminus1) due primar-ily to heating and cooling loads (74 000 kJ kgminus1 yminus1)artificial lighting (15 000 kJ kgminus1 yminus1) and circulatingpumps (640 kJ kgminus1 yminus1)
Focusingonenergy Shiina et al (2011) studyhydro-ponic urban lsquoplant factoriesrsquo (temperature controlledartificial lighting and humidity controlled) in Japanand show that the energy intensity of the productionresulted in estimated greenhouse emissions of 64 kgCO2e kgminus1 lettuce despite the operationrsquos high yieldsContinuing to use GHG emissions as a proxy for energydemand this compares with estimates of 02 and 09kg CO2e kgminus1 for lettuce from Michigan hoop housesand California open-field lettuce production (Plaweckiet al 2014) and ranges between 024minus262 kg CO2ekgminus1 for lettuce from European open field and hot-house production (Hospido et al 2009) MeanwhileGoldstein et al (2016a) compared cumulative energydemand of rooftop hydroponic greenhouse tomatoesand lsquoconventionalrsquo production and find the former tobe roughly ten times as energy intensivewith importantimplications for carbon footprint However switchingenergy source from the Massachusetts electricity gridto hydroelectric or solar PV makes rooftop hydroponicgreenhouse production less carbon intensive than con-ventional production
These demonstrate that are potential for trade-offswhenaddressingenvironmental footprints throughUAif focusing on a single performance metric (ie wateralone) Though as hydroponic growing systems canbe used in controlled protected and open-field grow-ing systems and with a wide selection of hydroponictechnology options available variation can be expectedin the yields and energy demand of hydroponic oper-ations this introduces uncertainty in applying these
13 Hydroponic systems are those that involve the culture of plantsin the absence of soil in a nutrient-supplemented water medium(lsquoHydroponicsrsquo in Anonymous 2017)
5
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
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Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
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16
Environ Res Lett 12 (2017) 125004
figures to specific contexts but underscores the needfor careful consideration in designing for energy andwater demand reduction
Alternative irrigation sourcesUrban agricultural systems provide an applicationfor rainwater collection as well as blackgreywater14all of which could reduce wastewater volumes andstormwater runoff and potentially improve surfacewater quality and decrease net energy use as a result (iedue to theavoidanceofUAirrigationwithpotablewaterand downstream wastewater treatment) As exampleswastewater treatment in California and Massachusettsis estimated to require on average 17 and 24 MJ mminus3respectively (US Environmental Protection Agency2008 Klein et al 2005) This has the potential to bereduced if conveyance and treatment requirementsare avoided through application of wastewater in UAFurther if stormwater can be diverted from treat-ment plants to UA in jurisdictions using combinedsewer systems energy demand as well as pollutantsto receiving bodies could be reduced In an extremecase substantial diversion of rainwater for UA fromlakes and rivers that ordinarily receive it could con-tribute to localregional ecosystem decline or surfacewater quality issues (Goldstein et al 2016a) Finallydepending on how UA is managed runoff from openfield urban farms could result in increased nutrientloads being passed down to receiving bodies or down-stream wastewater treatment plants (Pataki et al 2011)Upscaling UA could result in this being an additionalsource of non-point pollution for consideration by citymanagersplanners
Packaging materialsThe use of packaging materials can also potentially beavoided in UA operations in instances of productionfor personal consumption or within shorter distribu-tion chains such as when food is sold directly by theproducer (Garnett 1999) For example the climateimpacts of the embodied energyof polyethylene tereph-thalate clamshells and polystyrene trays that are oftenused in tomato packaging (again using carbon as aproxy for energy use) were estimated to be 25 and100 greater respectively per unit mass of tomatowhen compared to loose packaging (US Environmen-tal Protection Agency 2010) Still the authors notedthatmodifiedatmospherepackagingusingplasticshavebeen shown to increase shelf life by two or three timeswhich may reduce waste and consequently GHGsassociated with tomato production and disposal Thiswaste reduction could then offset the embodied energyneeded for the packaging material that provides thisadded shelf life
14 Blackwater refers to wastewater conveying faeces and urine whilegreywater includes other wastewater streams from human use thatdo not (ie dishwater shower water)
The use of packaging does not need to be anall or nothing proposition employing some packag-ing for various meal components can result in a netenergy savings (relative to lsquotypicalrsquo packaging con-figurations) when accounting for avoided waste andmarginal energy requirements semi-prepared mealsexamined by Hanssen et al (2017) were slightly moreenergy efficient when compared with those preparedfrom scratch It is generally important to recog-nize the embodied energy of the food products andpackaging materials being considered higher embod-ied energy food products (cheese beef bread) moreeasily justifying the additional energy inputs asso-ciated with packaging than unprocessed fruits andvegetables (Williams and Wikstrom 2011) Similarlythe application of plastic films and containers maybe more easily justified when compared with moreenergy-intensive materials such as steel aluminum orglass
Transportation and supply chain considerationsWhile UA and other forms of localization are oftenintuitively thought to reduce life cycle energy demandthe reality is more complicated (Webb et al 2013)Supply chains crossing a variety of artificial jurisdic-tional boundaries may in fact be more direct thanthose created by constraining agriculture within aregionstate depending on the product consump-tion point and regional characteristics (Nicholsonet al 2015) Broad-scale localization of agriculturehas the potential to increase transportation energyas well as associated GHG emissions relative to theconventional supply chain if definitions of local andimplications for modified supply networks includ-ing transport modes are not carefully consideredIndeed a commonly cited reason to pursue UA is toreduce energy-related impacts associated with trans-portation Estimates of transportationrsquos contributionto the food systemrsquos energy demand and GHG emis-sions have been estimated at approximately 10 orless (Weber and Matthews 2008 USDA ERS 2010Garnett 2011)
Numerous studies from the literature (Coley et al2009 Edwards-Jones et al 2008 Pirog et al 2001) havechallenged the common assumption that lsquolocalizingrsquofood production results in reduced transport energyuse and GHG emissions and effects on distributionnetworks need to be evaluated on a case basis to justifysuch a claim For instance transport-related impactsfor cheese shipped 20 000 km from New Zealand toconsumers inEnglandbyboatweredominatedby road-freight and consumer automobile use highlightingthe limitations of singular focus on transport distance(Basset-Mens et al 2007) The GHG implications ofexternal energy inputs to support year-round urbanfood production and their ability to overwhelm gainsachieved through reduced distribution distances mustbe considered in the context of upscaling of urban foodproduction
6
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Ackerman K Conard M Culligan P Plunz R Sutto M P andWhittinghill L 2014 Sustainable food systems for future citiesthe potential of urban agriculture Econ Soc Rev 45189ndash206
Albaho M Thomas B and Christopher A 2008 Evaluation ofhydroponic techniques on growth and productivity ofgreenhouse grown bell pepper and strawberry Int J Veg Sci14 23ndash40
Alexander C Ishikawa S Silverstein M Jacobson M King I F andAngel S 1977 A Pattern Language (New York OxfordUniversity Press)
Almeida J Achten W M J Verbist B Heuts R F Schrevens E andMuys B 2014 Carbon and water footprints and energy use ofgreenhouse tomato production in Northern Italy J Ind Ecol18 898ndash908
Althaus H-J 2003 Processmdashsteel production converter chromiumsteel 188 RER (EcoInvent Database Version 33)
Altieri M A Companioni N Canizares K Murphy C Rosset PBourque M and Nicholls C I 1999 The greening of thelsquobarriosrsquo urban agriculture for food security in Cuba AgricHuman Values 16 131ndash40
Amoah P Drechsel P Abaidoo R C and Henseler M 2007 Irrigatedurban vegetable production in Ghana microbiologicalcontamination in farms and markets and associated consumerrisk groups J Water Health 5 455ndash66
Andrews T Williams V and Dalmeny K 2017 Sustainable FoodCities (httpsustainablefoodcitiesorg)
Anonymous 2011 Aeroponics American Heritage Dictionary of theEnglish Language 5th edn (httpsearchcredoreferencecomcontententryhmdictenglangaeroponics0)
Anonymous 2017 Britannica Academic (wwwacademicebcom)Arup and C40 Cities 2014 Climate Action in MegacitiesminusC40 Cities
Baseline and Opportunities vol 2 (httpissuucomc40citiesdocsc40_climate_action_in_megacities)
Audsley E et al 1997 Harmonization of Environmental Life CycleAssessment for Agriculture AIR3-CT94-2028 CommunityResearch and Technological Development Programme in thefield of Agriculture and Agro-Industry Including Fisheries AIR3 (Brussels Belgium)
Barbosa G Gadelha F Kublik N Proctor A Reichelm L WeissingerE Wohlleb G and Halden R 2015 Comparison of land waterand energy requirements of lettuce grown using hydroponicvs conventional agricultural methods Int J Environ ResPublic Health 12 6879ndash91
Barthel S and Isendahl C 2013 Urban gardens agriculture andwater management sources of resilience for long-term foodsecurity in cities Ecol Econ 86 224ndash34
13
Environ Res Lett 12 (2017) 125004
Bass B and Baskaran B 2001 Evaluating rooftop and verticalgardens as an adaptation strategy for urban areas NationalResearch Council of Canada Report 46737 (wwwnpsgovtpssustainabilitygreendocsbasspdf)
Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Urban heat island mitigationThe predominance of dark (low-albedo) surfaces incities results in the absorptionof solar radiation andele-vated temperatures in and around urban areas raisingthe demand for cooling energy (the urban heat islandeffect Oke 1973) Urban agriculture could play a rolein attenuating this phenomenon by increasing surfacealbedo and the cooling effect of plant evapotranspi-ration (Ackerman et al 2014) Vegetation situated onbuildings has been shown to reduce individual build-ing cooling demands in Toronto Canada MadridSpainandLaRochelle France (Bass andBaskaran2001Saiz et al 2006 Jaffal et al 2012) Ackermann and col-leagues estimated that scaling up UA in New York Citycould reduce the local urban heat island by 22minus44(sim1 C) mitigating energy demands for cooling (Ack-erman 2012) The importance of this ancillary benefitof UA could become more important with the increas-ing frequency and severity of heat waves under likelyclimate change scenarios (Jansson 2013)
Impact of type of production system
Assuming UA may involve the use of protective struc-tures or controlled environments it is relevant toconsider the energy demand associated with such struc-tures Generally speaking open-field and protectedagriculture (eg hoop houses with no supplementalheating)havebeen found to require lower energy inputsthan heated systems (eg heated greenhouses) Studiesfocusing on open-field conventional tomato produc-tion in the US and the Mediterraneanhad energy inputsfor production of 140ndash280 MJ Mgminus1 (Brodt et al 2013Tamburini et al 2015) An average of three Moroc-can protected tomato operations had energy inputsof diesel and electricity for fertigation and pesticideapplication of 460 MJ Mgminus1 (Payen et al 2015) Withhothouse operations energy input can increase furtherwith a selection of studies focusing on tomato cultiva-tion showing energy inputs ranging from 425 28 50076 000 MJ Mgminus1 for case studies in Northern ItalyFrance and Iran respectively (Heidari and Omid 2011Boulard et al 2011 Almeida et al 2014) In the Frenchcase heated operations required six times more energyper unit of weight than the protected system (Boulard etal 2011) Goldstein et al (2016a) found similar patternsof variation for tomatoes depending on productionmethod with resource requirements presented intable 2 (modified here to present consistent units)
Nevertheless studies that directly comparecontrolled-environment growing with open-field agri-culture for certain crop typespresent amixedpicture Inone study Martınez-Blanco et al (2011) found that lifecycle cumulative energy inputs per Mg of protectivestructure greenhouse tomatoes produced in Catalo-nia was 13 greater when compared with open-fieldproduction (considering operations using mineral fer-tilizer inputs only) The additional energy demand
in the greenhouse operations is dominated by thegreenhouse structure in spite of some savings realizedthrough reduced cultivation-stage fertigation infras-tructure nursery plants and irrigation needs Howeverin an Indonsian case study Kuswardhani et al (2013)found that energy demand per unit mass was higherfor open-field tomato when compared to protectivestructure greenhouses but lower for lettuce this isattributed to higher fertilizer and pesticideherbicideneeds for open-field tomatoes (predominantly thelatter) whereas open-field lettuce had lower energyrequirements in spite of this higher demand (andhigher labor inputs) due to the substantial electricityrequirements for the drip irrigation system used in thegreenhouse lettuce Their study did not include theembodied energy of the greenhouse structure
Studies for tomato production in Antalya Turkeysuggest that energy requirements per kg yielded forprotective structure greenhouse tomato productionwere approximately 30 lower than that in open fields(Esengun et al 2007 Hatirli et al 2006) The greateryield coupled with lower labor machinery and irri-gation energy provide a net energy saving relative toopen fields in spite of greater fertilizer electricity andpesticide inputs for these greenhouses This study alsoexcludes embodied energy of greenhouse infrastruc-ture When taken together these studies suggest thatinputs required for UA will be operation crop andclimate dependent emphasizing the need for consider-ation of these elements when making comparisons andconsidering UA expansion
With respect to soilless production systems Albahoet al (2008) state that aeroponic15 systems require anuninterrupted electrical supply but it is unclear as towhether this energy demand is offset by lower inputsand higher yields relative to conventional controlled-environment or hydroponic systems A summary of theenergy implications of production methods is providedin table 3 along with estimates of energy implicationsfrom efforts to scale up UA in table 4
Drivers of variabilityJudging the pressures production systems haveon resource demands requires reflection on anumber of contextual factors For example localclimategeography may reduce the need for energy-intensive inputs (iemild climate plentiful surfacerainwater) As well existing infrastructure (green and grey)may or may not provide access to necessary inputs(nutrients water energy labor and growing media)This reflection may also include questions such aswhether there is an abundance of low-grade heat thatis accessible for exploitation and is the supplier (iea local utility) amenable to supporting its exploita-tion or perhaps if there is an existing agreement to
15 Aeroponic systems are those that involve the culture of plants inthe absence of soil or hydroponic media (Anonymous 2011)
7
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Table 3 Energy implications of different production methods
Production method Energy benefits Energy costs
Open airmdashlarge scale Reliant on natural systems for photosynthesis
growing environment and to some extent water
supply
Centralized and seasonal production
systems that tend to require complex
distribution networks that necessitate
transportation and cold storageOpen airmdashsmall scale (eg balconyallotment residential garden)
Reliant on natural systems for photosynthesis avoids
conventional distribution network
Input practices dependent on skill of
UA practitioner (potential for
excessive use) system design (eg
moisture retention of planter boxes
compared with field)Controlled environmentmdashprotectedagriculture
Higher yields can be located close to consumption
with an extended growing season low material inputs
relative to other
Relatively high embodied energy
inputs of capital per production unit
when compared with open fieldControlledenvironmentmdashconventionalgreenhouses
Higher yields can be located close to consumption
with an extended growing season
As above but with energy inputs for
lighting irrigation systems or other
control systems in addition to
growing mediumControlled environmentmdashadvancedsoilless systems
Higher yields can be located close to consumption
with an extended growing season
As above but with added operating
energy from soilless systems (eg
pumping dosing equipment)
Table 4 Estimated energy impacts within and beyond urban boundaries from scaling up urban agriculture on the broaderfoodndashenergyndashwater system
Within urban boundaries Beyond urban boundaries
Upward Pressure∙ Heating (for some controlled environment agriculture)∙ Waterwastewater treatment (conventional network usage)∙ Labor (paid or unpaid)∙ Transportation (in cases of inefficient local supply chain)
Upward Pressure
∙ Construction materials (eg steel framing LDPE sheeting
polycarbonate glazing)a b c
Downward Pressure∙ Transportation (eg backyard gardens)∙ Waste disposal (assuming less loss along supply chain)∙ Waterwastewater (decentralized usage)∙ Building energy demand (eg evapotranspiration green roofs)
Downward Pressure
∙ Irrigation water (through controlled-environment agriculture)
∙ Inorganic inputs (wastewater reuse)
∙ Machinerycapital (human inputs)
∙ Packaging materials
∙ Cold-chain requirements
a Goldstein et al (2016a)b Martınez-Blanco et al (2011)c Kulak et al (2013)
supply nutrients from wastewater to peri-urban agri-culture or further afield Additionally an abundanceof uncontaminated vacant land or a low populationdensity may make open-field or protected systems themost plausible approach Further considerations withrespect to publically-owned land might be whetherthese local green spaces are compatible with UA inte-gration when safety waste collection accessibility andpublic demand are taken into account Finally Pelletieret al (2011) suggest that scale of production systemsmay also play a role in energy efficiency though scalein itself is not an indicator of energy efficient produc-tion smaller operations have been observed to havelower energy intensities in the examples of tomatoesand swine It is clear that further research is needed toparse out the roles that scale climate existing infras-tructure waste resource availability can have on theoverall energy picture of UA operations Moreoveran assessment of the local context is necessary beforepromoting any particular UA approach along with theaccompanying resource demands these systems requirein a given context
Exploiting urban resources for localagriculture
Numerous opportunities exist to scale up UA in anenergy-efficient manner both within present urbansystems and carefully-planned future developmentsIf however an industrial ecology lens were appliedfor future planning a paradigm shift in food systemsintegration could be achieved with respect to the urbanfoodndashenergyndashwater system includingopportunities forutilizing food waste wastewater and waste heatCO2recovery In industrial ecology efforts are made tomimic natural ecosystems through more efficient use ofresources through the exploitation of waste streams byother production systems (Clift and Druckman 2016)
The urban form can be re-imagined to facilitatethe incorporation of UA in a truly integrated way Theconcept of co-locating agriculture would imply morethan preserving peri-urban agriculture and householdgardens it would focus on identifying spaces withinbuilt-up areas that are amenable to agriculture and thatare also within close proximity to agricultural inputs
8
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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16
Environ Res Lett 12 (2017) 125004
(waste heat compost wastewater and flue CO2 fromcompatible sources) One example of such an eco-industrial system in a rural setting is described by Zhanget al (2013) where yields can be improved from CO2fertilization through the integration of manure man-agement and greenhouse operations Biogas generatedfrom the manure disposal system is used in place of nat-ural gas to heat the greenhouses and fertilize with CO2while reducing emissions of GHGs and air pollutantsMetson et al (2012) demonstrate that the co-locationof agriculture near urban areas can enable improvedresource efficiency In their Arizona study they foundthat the increasing dairy demand from a growing citywas accompanied by an expansion of dairies and alfalfafarms (for feed) in its hinterlands the alfalfa farms uti-lized cow manure from the dairies as well as biosolidsfrom urban wastewater as a source of phosphorousincreasing the local nutrient cycling in the city-region Ifplanners are able to identify or (ideally) inventory pro-jectedcurrent UA-related resource streams the overallembodied or direct energy demand associated withthese UA systems can be reduced more deliberatelyand presumably more effectively
A summary of key resource streams that are valu-able in agriculture is provided in table 5 along withtheir conventional energy inputs as stated in a varietyof literature sources The extent to which these energydemands will be offset will differ depending on theagriculture operation
With the increasing frequency of extreme weatherevents and uncertainty of future water availabilityagriculture production in the US has the poten-tial to be negatively affected by climate change (USGlobal Change Research Program 2014) Urban agri-culture could increase resilience against these (as ithistorically has done during resource shocks throughthe centuries per Barthel and Isendahl 2013) whilereducing environmental impacts within the currentinfrastructural construct these benefits could be evengreater if an industrial ecology approach is takenIndeed controlled-environment production systemscan potentially protect crops from the climate vari-ability and extremes that would otherwise disturbopen-field production systems These more secureand higher yielding (Martınez-Blanco et al 2011)operations would bring greater certainty in yields aswell as improved resilience relative to the uncer-tainty of the broader food supply chain In additioncontrolled-environment agriculture systems can beplanned for integration into new and existing build-ings and industries to make better use of inputs thatare predominantly from urban waste streams (eg fluegas waste heat wastewater biosolids) The followingsections provide a discussion of strategies to deploycontrolled-environment agriculture within the currentinfrastructural context and within an interconnectedUA ecosystem that is designed for resource recoveryfrom waste streams
Energy production from food wasteFood waste has the potential to be converted to auseful energy resource in the form of biogas withmany cities already collecting source-separated organ-ics for processing in local anaerobic digesters (UckunKiran et al 2014 Sanscartier et al 2012 Moharebet al 2011 Bernstad and la Cour Jansen 2011) Fol-lowing the potential for circular resource use suggestedby Metson et al (2012) the proximity of increasedurban food waste from both production as well asfurther down the food supply chain could provide agreater feedstock for co-located urban anaerobic diges-tion (AD) systems In addition digestate producedfrom these facilities could find local end-uses in UAoperations facilitating a circular material flow Gov-ernments are currently promoting UA to reduce thecarbon footprint of cities (Arup and C40 Cities 2014)Keeping this objective in mind it is important to con-sider how food waste (a major component of GHGemissions from landfills US EPA 2017) can be betterutilized within a more cyclical UA system
Using foodwaste for energy generation throughADprovides an opportunity for distributed energy gener-ation while decreasing the impact of food waste ondownstream systems (landfills wastewater treatmentplants) Levis and Barlaz (2011) assessed the environ-mental performance of food waste disposal in ninecommon waste management systems and found thatAD performed best with respect to GHG emissionsNOx SO2 and net energy demand Further consid-ering the proximity to potential end users the useof biogas from AD facilities for both heat and elec-tricity production could become more economicallyattractive in an urban context especially with local UAconsumers of waste CO2 (from biogas production) andAD digestate It is estimated that the US cities produce130 Mt of food waste annually16 Using estimates of 184kWh of electricity and 810 MJ heat Mgminus1 of wet waste(from Moslashller et al 2009) this quantity of food wastehas the potential to provide electricity for 72 millionNissan Leaf all-electric vehicles17 and the equivalentheatingdemand forover15millionMichiganhomes18 respectively
Cities are currently operating AD facilities that areproviding energy to the broader community Barcelonais treating 192 000 t yrminus1 of its organic fraction ofmunicipal solid waste (OFMSW) through AD having apositive energy balance of around 22 MJ producedMJconsumed at the facility from pre-treatments anddigester pumpingstirring (Romero-Guiza et al 2014)
16 Uses an estimate of 500 kg of food discarded per capita in 2010from retail and consumers (USDA ERS 2013) and a US urbanpopulation of 261 427 500 (US Census Bureau 2015)17 Assuming 11 500 miles per year (Heller and Keoleian 2015) Leafmileage of 29 kWh100 miles (wwwfueleconomygov)18 The average Michigan home consumes 123 million BTU 55for heating (wwweiagovconsumptionresidentialreports2009state_briefspdfmipdf)
9
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Table 5 Key agricultural resource streams potential urban sources and energy requirement for resource stream use in conventional urbanagricultural systems
Urban resource stream Potential alternative urbansources
Energy requirementminusconventional sources
Source of energy requirementdata
Treated water ∙ Decentralized wastewater
treatment
∙ Rain barrels
∙ Grey water
133minus140 MJ mminus3 (surface
water)
sim173 MJ mminus3 (groundwater)
Electric Power Research
Institute (2002)
Heat and carbondioxidea
∙ Electricity generation
∙ Residential furnaces boilers
hot water heaters
∙ Industrialcommercial waste
heat
∙ Anaerobic digesters
∙ Heat transferred from
conditions buildings
∙ Sewage networks
sim2500 kWh mminus2-year (mild
climate eg HDD18 = 2800
Abbotsford BCe greenhouse
heated with natural gas)
Calculated from British
Columbia case study (Zhang
et al 2013)
Nitrogen 138 MJ kgminus1 (345
NH4NO3)
145 MJ kgminus1 (NH4SO4)
151 MJ kgminus1 (275
NH4NO3)
3258 MJ kgminus1 (CH4N2O)c
EU averageminus3528 MJ kgminus1
(urea) bestminus184 MJ kgminus1
5746 MJ kgminus1 (US)
Feedstockminus2552minus2765 MJ
kgminus1 (UK) indirect and direct
energymdash84minus196 MJ kgminus1
(UK)
Audsley et al (1997) Danish
and UK data
Smith et al (2001)
West and Marland (2002)
Mortimer et al
(2003)mdashNH4NO3
appendix C
Phosphorus ∙ Digestate from anaerobic
digestion
∙ Human biosolids
∙ Animal manure
∙ Compost (ie using wastes from
gardens green roofs and UA)
∙ Industrial waste streams
382 MJ kgminus1
972minus1872 MJ kgminus1 (EU)
EU averageminus3622 MJ kgminus1
bestminus182 MJ kgminus1 (P2O5)
702 MJ kgminus1 (P2O5) (US)
1580 MJ kgminus1 (P2O5) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Potassium 054 MJ kgminus1
500 MJ kgminus1d
EU averageminus1120 MJ kgminus1
bestminus058 MJ kgminus1 (K2O)
684 MJ kgminus1 (K2O) (US)
929 MJ kgminus1 (K2O) (EU)
Hansen (2006)b
Audsley et al (1997)
Smith et al (2001)
West and Marland (2002)
Elsayed et al (2003)
Calcium 173 MJ kgminus1 (CaCO3) (US)
209 MJ kgminus1 (CaO) (EU)
West and Marland (2002)
Elsayed et al (2003)
Structural materials ∙ Municipal solid waste for
construction materials (eg
hoop houses)
011 MJ kgminus1 steel (for hoop
house or greenhouse
structures)
Althaus (2003) - EcoInvent 3
Life Cycle Inventories of
Metals 2009
a to be diverted to boost yields of greenhouse operationsb excludes lsquoinherentrsquo (embodied) energy of CH4 305 MJ kgminus1 Nc including mining energy demand as reported in Boslashckman et al 1990d sum of natural gas electricity and coke used in manufacture of chromium steele five-year average (2012ndash16) from wwwdegreedaysnet
Additionally anaerobic co-digestion with sewagesludge could enhance biogas production and deals withthe seasonality that food waste from UA can present(Fonoll et al 2015 Shrestha et al 2017) Policy inter-ventions will likely be necessary to encourage broaderinvestment in AD (Binkley et al 2013) For example inthe north of Italy 26 000ndash28 000 of OFMSW are treatedeach year in AD plant while the facility has obtaineda positive cash flow of e25 million yrminus1 an incentive
for the usegeneration of renewable energy was neededto enable this to occur (Riva et al 2014)
Beyond energy production AD offers additionalbenefits Situating anaerobic digesters near UA oper-ations could facilitate the reuse of digestate (such asin Garfı et al 2011) saving on fertilizer requirementsand reducing transportation costs for waste diversionThe coupling of AD with pyrolysis has the potential toproduce biochar which could be used to improve soil
10
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
References
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Ackerman K Conard M Culligan P Plunz R Sutto M P andWhittinghill L 2014 Sustainable food systems for future citiesthe potential of urban agriculture Econ Soc Rev 45189ndash206
Albaho M Thomas B and Christopher A 2008 Evaluation ofhydroponic techniques on growth and productivity ofgreenhouse grown bell pepper and strawberry Int J Veg Sci14 23ndash40
Alexander C Ishikawa S Silverstein M Jacobson M King I F andAngel S 1977 A Pattern Language (New York OxfordUniversity Press)
Almeida J Achten W M J Verbist B Heuts R F Schrevens E andMuys B 2014 Carbon and water footprints and energy use ofgreenhouse tomato production in Northern Italy J Ind Ecol18 898ndash908
Althaus H-J 2003 Processmdashsteel production converter chromiumsteel 188 RER (EcoInvent Database Version 33)
Altieri M A Companioni N Canizares K Murphy C Rosset PBourque M and Nicholls C I 1999 The greening of thelsquobarriosrsquo urban agriculture for food security in Cuba AgricHuman Values 16 131ndash40
Amoah P Drechsel P Abaidoo R C and Henseler M 2007 Irrigatedurban vegetable production in Ghana microbiologicalcontamination in farms and markets and associated consumerrisk groups J Water Health 5 455ndash66
Andrews T Williams V and Dalmeny K 2017 Sustainable FoodCities (httpsustainablefoodcitiesorg)
Anonymous 2011 Aeroponics American Heritage Dictionary of theEnglish Language 5th edn (httpsearchcredoreferencecomcontententryhmdictenglangaeroponics0)
Anonymous 2017 Britannica Academic (wwwacademicebcom)Arup and C40 Cities 2014 Climate Action in MegacitiesminusC40 Cities
Baseline and Opportunities vol 2 (httpissuucomc40citiesdocsc40_climate_action_in_megacities)
Audsley E et al 1997 Harmonization of Environmental Life CycleAssessment for Agriculture AIR3-CT94-2028 CommunityResearch and Technological Development Programme in thefield of Agriculture and Agro-Industry Including Fisheries AIR3 (Brussels Belgium)
Barbosa G Gadelha F Kublik N Proctor A Reichelm L WeissingerE Wohlleb G and Halden R 2015 Comparison of land waterand energy requirements of lettuce grown using hydroponicvs conventional agricultural methods Int J Environ ResPublic Health 12 6879ndash91
Barthel S and Isendahl C 2013 Urban gardens agriculture andwater management sources of resilience for long-term foodsecurity in cities Ecol Econ 86 224ndash34
13
Environ Res Lett 12 (2017) 125004
Bass B and Baskaran B 2001 Evaluating rooftop and verticalgardens as an adaptation strategy for urban areas NationalResearch Council of Canada Report 46737 (wwwnpsgovtpssustainabilitygreendocsbasspdf)
Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
fertility (Monlau et al 2016) Excess heat from AD orpyrolysis can also be applied to the digester to or todistrict heating systems and can be used to heat housesor aquaculture operations
The barriers associated with the reintroduction oflivestock into relatively dense areas are formidablethese include local regulations public health concernsand logistic difficulties of feed provision (Food andAgriculture Organization 2001 Butler 2011) If sur-mounted these operations as well as primary andsecondary food processing industries (eg breweriesethanol production harvest-related waste from agri-cultural operations) can provide substantial feedstocksfor AD
Finally in cases where AD is impractical UAprovides a local end user for composted residuesHence onsite compost facilities could be a compo-nent of future UA operations This would reduceGHG emissions from waste that would have beendisposed of in a landfill and avoids the need fortransportation of waste to a location offsite Accord-ing to the US EPA WARM model19 composting foodwaste and avoiding its addition to landfill results ina net reduction of 096 Mg CO2e per Mg of foodwaste
Wastewater reuse in urban agricultureBoth solid and liquid streams of wastewater are anunderutilized resource with their current perceptionas a municipal liability requiring resource-intensivetreatment and disposal It has been estimated thatapproximately 2 of the total US electricity use isfor municipal wastewater treatment (Electric PowerResearch Institute 2002) The aeration step of treat-ment which promotes biodegradation of pollutantsaccounts for approximately 50 of this energy use(Curtis 2010 Mamais et al 2015) This approach alsoresults in the release of GHG emissions to the atmo-sphere in 2000 US wastewater treatment resulted insim333 Mt CO2e from energy use and sludge degrada-tion (Center for Sustainable Systems 2014) A systemthat diverts wastewater from treatment reduces thelevel of treatment or eliminates the need for aeration(through diversion from receiving water bodies to UA)could help reduce these emissions
Wastewater reuse could be a practical source ofwater and nutrients in UA Previous studies havenoted heavy metal and pathogen contamination ofwastewater-irrigated produce (Amoah et al 2007Khan et al 2008) underscoring the need to ensureregulatory requirements for irrigation water qual-ity are met (World Health Organization 2006) Ifcitiesneighborhoods were to reorient their wastew-ater treatment goals from a focus on disposal toone of reuse the treatment reduction could result
19 Using national average landfill characteristics and default wastehauling distances of 20 miles (www3epagovwarm)
in substantial energy savingsmdashdirectly at the pointof treatment as well as upstream from crop pro-duction For example crops grown using waterand nutrients recovered from wastewater could off-set the embodied energy demand of crops thatare grown elsewhere using more energy-intensiveirrigation water and inorganic fertilizers Anaero-bic membrane bioreactors are one technology thathas been proposed to accomplish these goals (Smithet al 2012 2014) recovering energy generating aneffluent rich in nutrients and low in suspended solidsand organics and eliminating energy requirementsrelated to aerobic treatment (Smith et al 2014) Regard-less of the technology used further research is necessaryto evaluate the removal potential of trace contaminantsand viral pathogens prior to reuse for UA (Smithet al 2012 McCurry et al 2014) By taking an indus-trial ecology approach residential waste streams andindustrial waste streams that are relatively benign andwith a low pathogen load (eg brewery waste) couldbe used in subsurface irrigation of UA crops avoidingconventional treatment and reclaiming nutrients forfood production
Waste heat or CO2 use for urban agricultureFinally a further industrial ecological approach wouldsee conventional infrastructure systems integrated withagriculture to increase productivity Many sourcesof waste heat and CO2 exist within the urbanboundary from residences to industrial operations toelectrical utilities Where natural gas is employed inthese applications greenhouse operations can utilizethe relatively clean exhausted low-grade energy asa heat source as well as CO2 for crop fertilization(Kimball 1983 Mortensen 1987) If greenhouses andhouseholds could be integrated there is a potentialefficiency gain in the combined system over its dis-crete components including through the provision ofCO2 for crop fertilization and utilization of waste heatA number of studies have suggested that building-integrated agriculture has the potential to improveoverall energy performance of the system (Spechtet al 2013) Decentralized residential heating systems insingle-family homes make utilization challenging butspecialized building-integrated systems like the exam-ple developed by Seawater Greenhouses could be amodel for smaller-scale units that utilize waste heatand CO2 on site (Delor 2011) Nevertheless the modelpresented by Ceron-Palma et al (2012) of a rooftopgreenhouse in Barcelona highlights the challenges ofbuilding-integratedUAasgreenhouseheating require-ments were not temporally aligned with the times ofexcessheatwithin thebuilding instead this typeof pro-duction system may be better suited to colder climateswhere exhaust CO2 and heat from boilersfurnaces aremore available during winter months This highlightsthe need for additional research on how to overcomethese types of management issues to support greaterresource efficiency
11
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
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16
Environ Res Lett 12 (2017) 125004
Planningandhumancapital considerations forurbanagricultureHistorically UA was a natural part of urban develop-ment and eventually an essential component of theplans of early urban planning practitioners (Vitielloand Brinkley 2013) However UA was not a primaryobjective for planning developed-world public spacesin industrialized food system of 20th century citiesCalls to reconsider the value of UA have been madefor decades (eg in the pattern language proposedby Alexander et al 1977) and planning for UA as aresult has returned The success of UA re-adoptionin urban design is demonstrated by the Carrot CityInitiative (Gorgolewski et al 2017) which facilitates dis-cussions on urban design for food production Theseand other resources can help to increase the sophis-tication of food planning in a more cyclical urbanecosystem
Planners can open up or create space to enablethe upscaling of UA in either building-integrated sys-tems or newexisting green space For example parkscould be redeveloped from being merely aesthetically-pleasing recreational landscapes to be more functionalwith edible productivity through the incorporation offruit trees and community gardens Inventories of suit-able public and private vacant land could be identifiedfor UA use through geomatic methods (McClintocket al 2013) Municipal support for training in theharvest and processing of crops could increase thepublicrsquos awareness of the resources embodied withinthe food they consume and minimize and potentiallyminimize crop waste Processing infrastructure suchas fruit presses or preserving facilities could be situ-ated within the parkrsquos borders By-laws could be put inplace to incentivize rooftop UA as has been done withgreen roofs in some cities (eg Toronto and ChicagoLoder 2014)
As mentioned previously UA expansion couldlead to local increases in polluted run-off This mayrequire the implementation of by-laws restrictingfertilizer or pesticide application storm water reme-diationmitigation measures and out-reach to informcitizens of health and environmental implications ofagriculture As well inventories of UA and surveysof practices coupled with geographic information sys-tems could help planners identify potential hotspots forrunoff odors or other impacts
Human labor is an abundant urban resource that isanticipated to become more available in cities as trendsof urbanization and automation progress Smaller-scale agricultural systems have the potential to utilizethis labor as they tend to be more labor intensivethan conventional mechanized open-field agricultureAs well the integration of UA in buildings and theapplication of advanced production approaches (iesoilless operations) require specialized training duringdesign construction and operation creating high-skilled employment opportunities The impacts onfood prices by shifting to small-scale UA systems is
unclear the 2012 US agricultural census suggests thathired and contract farm labor contributed to only102 of total farm production expenses though itis suggested that this would vary substantially by cropraised and potentially less mechanizedautomated sys-tems (US Department of Agriculture 2014 USDA ERS2014) The recreational utility realized by those pur-suing UA as a leisure activity could reduce the netincrease in costs (ie people providing free labor in pur-suit of UA as a hobby) further multiple non-monetarybenefits (civic engagement social cohesion food secu-rity) have been recognized enabling a scenario wherebroad public benefits of UA can be realized coupledwith an understanding of its effects on health and theenvironment (Chen 2012 Horst et al 2017)
Avoiding unintended consequences in scaling upurban agricultureA number of issues may inhibit efforts to scale upUA including land scarcity (Martellozzo et al 2014)UArsquos uncertain contribution to food security (Ward2015) environmental impacts of decentralized pro-duction (Nicholson et al 2015 Coley et al 2009) andmanagement of new sources of food waste (Levis andBarlaz 2011 Forkes 2007 Smil 2004) Avoiding unin-tended consequences and continued inefficiency in thefood system through urban production requires a plan-ning approach that coordinates input streams reducespotential for waste and enables co-location to mitigategrowth in transportation demand Foley et al (2011)suggest that efforts to meet the food needs of the risingglobal (urban) population face substantial challenges toenvironmental protection Further resource demandsof all urban food consumption far exceeds the resourcesthat can be provided within city boundaries and mov-ing towards this goal could create new local resourcestresses for example Ramaswami et al (2017) demon-strate this situation for New Delhirsquos water demandwhere water used for food production represented 72of urban-related withdrawals (in turn only 14 ofthese water withdrawals was provided within the cityrsquosboundary)
We argue that an industrial ecological approachto UA has the potential to slow land use change(through the intensification of production) increasecrops yields (by increasing management intensity)increase resource efficiency (through co-location ofinputs from waste streams) and encourage low-carbondiets (through increasedaccess to freshproduceWake-field et al 2007 Schafft et al 2009) However proximityalone are not a guarantee for success of eco-industrialUAGibbs andDeutz (2007) reviewanumberof unsuc-cessful industrial ecological case studies and interviewparticipants in these and find that results often do notmatch objectives However with an incremental plan-ning approach improved networking to develop trustand cooperation and targeted policy interventions bymunicipalities could improve the success of industrialecological approaches
12
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
References
Ackerman K 2012 The potential for urban agriculture in New YorkCity growing capacity food security and green infrastructureReport (New York Columbia University Urban Design Lab)(httpurbandesignlabcolumbiaedufiles2015044_urban_agriculture_nycpdf)
Ackerman K Conard M Culligan P Plunz R Sutto M P andWhittinghill L 2014 Sustainable food systems for future citiesthe potential of urban agriculture Econ Soc Rev 45189ndash206
Albaho M Thomas B and Christopher A 2008 Evaluation ofhydroponic techniques on growth and productivity ofgreenhouse grown bell pepper and strawberry Int J Veg Sci14 23ndash40
Alexander C Ishikawa S Silverstein M Jacobson M King I F andAngel S 1977 A Pattern Language (New York OxfordUniversity Press)
Almeida J Achten W M J Verbist B Heuts R F Schrevens E andMuys B 2014 Carbon and water footprints and energy use ofgreenhouse tomato production in Northern Italy J Ind Ecol18 898ndash908
Althaus H-J 2003 Processmdashsteel production converter chromiumsteel 188 RER (EcoInvent Database Version 33)
Altieri M A Companioni N Canizares K Murphy C Rosset PBourque M and Nicholls C I 1999 The greening of thelsquobarriosrsquo urban agriculture for food security in Cuba AgricHuman Values 16 131ndash40
Amoah P Drechsel P Abaidoo R C and Henseler M 2007 Irrigatedurban vegetable production in Ghana microbiologicalcontamination in farms and markets and associated consumerrisk groups J Water Health 5 455ndash66
Andrews T Williams V and Dalmeny K 2017 Sustainable FoodCities (httpsustainablefoodcitiesorg)
Anonymous 2011 Aeroponics American Heritage Dictionary of theEnglish Language 5th edn (httpsearchcredoreferencecomcontententryhmdictenglangaeroponics0)
Anonymous 2017 Britannica Academic (wwwacademicebcom)Arup and C40 Cities 2014 Climate Action in MegacitiesminusC40 Cities
Baseline and Opportunities vol 2 (httpissuucomc40citiesdocsc40_climate_action_in_megacities)
Audsley E et al 1997 Harmonization of Environmental Life CycleAssessment for Agriculture AIR3-CT94-2028 CommunityResearch and Technological Development Programme in thefield of Agriculture and Agro-Industry Including Fisheries AIR3 (Brussels Belgium)
Barbosa G Gadelha F Kublik N Proctor A Reichelm L WeissingerE Wohlleb G and Halden R 2015 Comparison of land waterand energy requirements of lettuce grown using hydroponicvs conventional agricultural methods Int J Environ ResPublic Health 12 6879ndash91
Barthel S and Isendahl C 2013 Urban gardens agriculture andwater management sources of resilience for long-term foodsecurity in cities Ecol Econ 86 224ndash34
13
Environ Res Lett 12 (2017) 125004
Bass B and Baskaran B 2001 Evaluating rooftop and verticalgardens as an adaptation strategy for urban areas NationalResearch Council of Canada Report 46737 (wwwnpsgovtpssustainabilitygreendocsbasspdf)
Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Implications of UA on production inputs foodwaste and transportation (of both labor and food prod-ucts) are dependent on UA approaches taken As anillustration this will be influenced by the productionpractices of UA practitioners efficiency of distributionsystems public and active transportation options foraccessing UA sites producer and retail practices forfood disposal and local attitudes towards food wasteAll of these require further study within each localcontext
Conclusions
This review has examined UA through a novel lensconsidering the energy implications of promoting theexpansion of food production in various forms withincities in advanced economies Scaling up UA has impli-cations for thebroader energy systemwith thepotentialto affect direct and upstream energy demand andenable the utilization of resources to a greater degreeThis review underscores the need to pursue furthercase study research to understand the implicationsof human and physical geographies on net energydemands and other environmental impacts of UA inits many iterations Different combinations of croptype climate production methodscale availability oflsquowastersquo resources co-locationapproaches and intensityofproductionallneed tobeexplored toobtainabroaderunderstanding of the life cycle energy implications ofscaling up urban agriculture
We have proposed and provide supporting infor-mation for a resource-efficient path to pursuing theexpansion of UAmdashthrough the exploitation of cropand other food wastes reuse of municipal wastewaterand biosolids for crop fertilization and irrigation andemploying the plentiful sources of waste heat and CO2Integrating agriculture with urban planning is not anew concept but deep consideration of energy use inthe broader food system and the availability of rele-vant resources within cities (often as underexploitedwaste streams) can help realize substantial efficiencyimprovements in future urbanized food system
Acknowledgments
This research was initiated through work completedduring the National Science Foundation (NSF grantnumber 1541838) funded workshop held October5minus6 at the University of Michigan entitled lsquolsquoScalingrsquoUp Urban Agriculture to Mitigate Food-Energy-Water-Impactsrsquo XF and LR acknowledge supportfrom the NSF Sustainability Research Networks grant1444745 and REFRESCH (Global Challenges forthe Third Century program Office of the ProvostUniversity of Michigan) The authors thank GlenDaigger Tim Dixon Nancy Love Josh Newell andMartin Sexton for comments on various iterations ofthis manuscript
ORCID iDs
Eugene Mohareb httpsorcidorg0000-0003-0344-2253Martin Heller httpsorcidorg0000-0001-9204-6222PaigeNovak httpsorcidorg0000-0001-9054-0278Benjamin Goldstein httpsorcidorg0000-0003-0055-1323Xavier Fonoll httpsorcidorg0000-0003-3304-2437Lutgarde Raskin httpsorcidorg0000-0002-9625-4034
References
Ackerman K 2012 The potential for urban agriculture in New YorkCity growing capacity food security and green infrastructureReport (New York Columbia University Urban Design Lab)(httpurbandesignlabcolumbiaedufiles2015044_urban_agriculture_nycpdf)
Ackerman K Conard M Culligan P Plunz R Sutto M P andWhittinghill L 2014 Sustainable food systems for future citiesthe potential of urban agriculture Econ Soc Rev 45189ndash206
Albaho M Thomas B and Christopher A 2008 Evaluation ofhydroponic techniques on growth and productivity ofgreenhouse grown bell pepper and strawberry Int J Veg Sci14 23ndash40
Alexander C Ishikawa S Silverstein M Jacobson M King I F andAngel S 1977 A Pattern Language (New York OxfordUniversity Press)
Almeida J Achten W M J Verbist B Heuts R F Schrevens E andMuys B 2014 Carbon and water footprints and energy use ofgreenhouse tomato production in Northern Italy J Ind Ecol18 898ndash908
Althaus H-J 2003 Processmdashsteel production converter chromiumsteel 188 RER (EcoInvent Database Version 33)
Altieri M A Companioni N Canizares K Murphy C Rosset PBourque M and Nicholls C I 1999 The greening of thelsquobarriosrsquo urban agriculture for food security in Cuba AgricHuman Values 16 131ndash40
Amoah P Drechsel P Abaidoo R C and Henseler M 2007 Irrigatedurban vegetable production in Ghana microbiologicalcontamination in farms and markets and associated consumerrisk groups J Water Health 5 455ndash66
Andrews T Williams V and Dalmeny K 2017 Sustainable FoodCities (httpsustainablefoodcitiesorg)
Anonymous 2011 Aeroponics American Heritage Dictionary of theEnglish Language 5th edn (httpsearchcredoreferencecomcontententryhmdictenglangaeroponics0)
Anonymous 2017 Britannica Academic (wwwacademicebcom)Arup and C40 Cities 2014 Climate Action in MegacitiesminusC40 Cities
Baseline and Opportunities vol 2 (httpissuucomc40citiesdocsc40_climate_action_in_megacities)
Audsley E et al 1997 Harmonization of Environmental Life CycleAssessment for Agriculture AIR3-CT94-2028 CommunityResearch and Technological Development Programme in thefield of Agriculture and Agro-Industry Including Fisheries AIR3 (Brussels Belgium)
Barbosa G Gadelha F Kublik N Proctor A Reichelm L WeissingerE Wohlleb G and Halden R 2015 Comparison of land waterand energy requirements of lettuce grown using hydroponicvs conventional agricultural methods Int J Environ ResPublic Health 12 6879ndash91
Barthel S and Isendahl C 2013 Urban gardens agriculture andwater management sources of resilience for long-term foodsecurity in cities Ecol Econ 86 224ndash34
13
Environ Res Lett 12 (2017) 125004
Bass B and Baskaran B 2001 Evaluating rooftop and verticalgardens as an adaptation strategy for urban areas NationalResearch Council of Canada Report 46737 (wwwnpsgovtpssustainabilitygreendocsbasspdf)
Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Bass B and Baskaran B 2001 Evaluating rooftop and verticalgardens as an adaptation strategy for urban areas NationalResearch Council of Canada Report 46737 (wwwnpsgovtpssustainabilitygreendocsbasspdf)
Basset-Mens C McLaren S J and Ledgard S 2007 Exploring acomparative advantage for New Zealand cheese in terms ofenvironmental performance LCA Foods Conference 5th IntConf (Gothenburg Sweden 26 April)
Bernstad A and la Cour Jansen J 2011 A life cycle approach to themanagement of household food wastemdasha Swedish full-scalecase study Waste Manage 31 1879ndash96
Binkley D Harsh S Wolf C A Safferman S and Kirk D 2013Electricity purchase agreements and distributed energypolicies for anaerobic digesters Energy Policy 53 341ndash52
Boslashckman O C Kaarstad O Lie O H and Richards I 1990Agriculture and Fertilizers (Oslo Norsk Hydra)
Boulard T Raeppel C Brun R Lecompte F Hayer F Carmassi Gand Gaillard G 2011 Environmental impact of greenhousetomato production in France Agron Sustain Dev 31 757ndash77
Brodt S Kramer K J Kendall A and Feenstra G 2013 Comparingenvironmental impacts of regional and national-scale foodsupply chains a case study of processed tomatoes Food Policy42 106ndash14
Butler W H 2011 Welcoming animals back to the city navigatingpublic health tensions of urban livestock to achieve healthyand resilient communities J Agric Food Syst CommunityDev 2 193ndash215
Canning P Charles A Huang S Polenske K R and Waters A 2010Energy use in the US food system Research Report 94(Washington DC USDA ERS) (wwwersusdagovpublicationspub-detailspubid=46377)
Carol M 2010 Ontariorsquos water-energy nexus will we find ourselvesin hot water or tap into opportunity (Toronto POLISResearch) Report 10-01 (httppolisprojectorgfilespub_databasenexus-report_finalpdf)
Center for Sustainable Systems 2014 US Wastewater Treatment(Ann Arbor) (httpcsssnreumicheducss_docCSS04-14pdf)
Ceron-Palma I Sanye-Mengual E Oliver-Sola J Montero J-I andRieradevall J 2012 Barriers and opportunities regarding theimplementation of rooftop ecogreenhouses (RTEG) inMediterranean cities of Europe J Urban Technol 19 1ndash17
Chen S 2012 Civic agriculture towards a local food web forsustainable urban development APCBEE Procedia 1 169ndash76
Clift R and Druckman A 2016 Industrial ecologyrsquos first decadeTaking Stock of Industrial Ecology ed R Clift and A Druckman(London Springer) ch 1 p 373
Coley D Howard M and Winter M 2009 Local food food milesand carbon emissions a comparison of farm shop and massdistribution approaches Food Policy 34 150ndash5
Curtis T P 2010 Low-energy wastewater treatment strategies andtechnologies Environmental Microbiology 2nd edn ed RMitchell and J D Gu (Hoboken NJ Wiley-Blackwell)
Delor M 2011 Current state of building-integrated agriculture itsenergy benefits and comparison with green roofsminussummaryReport (httpbitly1ihZebG)
Despommier D 2013 Farming up the city the rise of urban verticalfarms Trends Biotechnol 31 388ndash9
Edwards-Jones G et al 2008 Testing the assertion that lsquolocal food isbestrsquo the challenges of an evidence based approach TrendsFood Sci Technol 19 265ndash74
Electric Power Research Institute 2002 Water and sustainability USElectricity Consumption for Water Supply and TreatmentndashtheNext Half Century vol 4 (Palo Alto CA EPRI) (wwwcircleofblueorgwp-contentuploads201008EPRI-Volume-4pdf)
Elsayed M A Matthews R and Mortimer N D 2003 Carbon andEnergy Balances for a Range of Biofuels OptionsmdashProjectNumber BB600784REP URN 03836
Energy Information Administration 2010 Trends in US residentialnatural gas consumption (wwweiagovpuboil_gasnatural_gasfeature_articles2010ngtrendsresidconngtrendsresidconpdf)
Esengun K Erdal G Gunduz O and Erdal H 2007 An economicanalysis and energy use in stake-tomato production in Tokatprovince of Turkey Renew Energy 32 1873ndash81
Foley J A et al 2011 Solutions for a cultivated planet Nature 478337ndash42
Fonoll X Astals S Dosta J and Mata-Alvarez J 2015 Anaerobicco-digestion of sewage sludge and fruit wastes evaluation ofthe transitory states when the co-substrate is changed ChemEng J 262 1268ndash74
Food and Agriculture Organization 2013 Climate-SmartAgriculture Sourcebook (wwwfaoorgdocrep018i3325ei3325e00htm)
Food and Agriculture Organization 2010 FAO Statistical Yearbook(wwwfaoorgdocrep015am081mam081m00htm)
Food and Agriculture Organization 2001 Stakeholders systemsand issues in urban livestock keeping Livestock Keeping inUrban Areas (wwwfaoorgdocrep004y0500ey0500e00htmtoc)
Forkes J 2007 Nitrogen balance for the urban food metabolism ofToronto Canada Resour Conserv Recycles 52 74ndash94
Francis C Hansen T Fox A Hesje P Nelson H Lawseth A andEnglish A 2012 Farmland conversion to non-agricultural usesin the US and Canada current impacts and concerns for thefuture Int J Agron Sust 10 8ndash24
Garfı M Gelman P Comas J Carrasco W and Ferrer I 2011Agricultural reuse of the digestate from low-cost tubulardigesters in rural Andean communities Waste Manage 312584ndash9
Garnett T 1997 Farming the city the potential for urban agricultureEcologist 26 299ndash307
Garnett T 1999 Urban agriculture in London rethinking our foodeconomy Report (wwwruaforgsitesdefaultfilesLondon_1PDF)
Garnett T 2011 Where are the best opportunities for reducinggreenhouse gas emissions in the food system (including thefood chain) Food Policy 36 S23ndash32
Gibbs D and Deutz P 2007 Reflections on implementing industrialecology through eco-industrial park development J CleanProd 15 1683ndash95
Goldstein B Hauschild M Fernandez J and Birkved M 2017Contributions of local agriculture to urban sustainability inthe Northeast United States Environ Sci Technol 517340ndash9
Goldstein B Hauschild M Fernandez J and Birkved M 2016aTesting the environmental performance of urban agricultureas a food supply in northern climates J Clean Prod 135984ndash94
Goldstein B Hauschild M Fernandez J and Birkved M 2016bUrban versus conventional agriculture taxonomy of resourceprofiles a review Agron Sustain Dev 36 9
Gorgolewski M Komisar J and Nasr J 2017 Carrot City Initiative(wwwryersoncacarrotcity)
Grard B J-P et al 2015 Recycling urban waste as possible use forrooftop vegetable garden Futur Food J Food Agric Soc 321ndash34
Grewal S S and Grewal P S 2012 Can cities become self-reliant infood Cities 29 1ndash11
Hamilton A J Burry K Mok H-F Barker S F Grove J R andWilliamson V G 2013 Give peas a chance Urban agriculturein developing countries A review Agron Sustain Dev 3445ndash73
Hamm M W 2015 Feeding citiesmdashwith indoor vertical farms FoodClim Res Netw (httpfcrnorgukfcrn-blogsmichaelwhammfeeding-cities-indoor-vertical-farms)(Accessed 6 September 2017)
Hansen T L 2006 Life cycle modelling of environmental impacts ofapplication of processed organic municipal solid waste onagricultural land (Easewaste) Waste Manage Res 24153ndash66
Hanssen O J Vold M Schakenda V Tufte P A Moslashller H Olsen NV and Skaret J 2017 Environmental profile packagingintensity and food waste generation for three types of dinnermeals J Clean Prod 142 395ndash402
14
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Hatirli S A Ozkan B and Fert C 2006 Energy inputs and crop yieldrelationship in greenhouse tomato production Renew Energy31 427ndash38
Heidari M D and Omid M 2011 Energy use patterns andeconometric models of major greenhouse vegetableproductions in Iran Energy 36 220ndash5
Heller M C and Keoleian G A 2015 Greenhouse gas emissionestimates of US dietary choices and food loss J Ind Ecol 19291ndash401
Horst M McClintock N and Hoey L 2017 The intersection ofplanning urban agriculture and food justice a review of theliterature J Am Plan Assoc 83 277ndash95
Hospido A Mila I Canals L McLaren S Truninger MEdwards-Jones G and Clift R 2009 The role of seasonality inlettuce consumption a case study of environmental and socialaspects Int J Life Cycle Assess 14 381ndash91
Howe J and Wheeler P 1999 Urban food growing the experience oftwo UK cities Sustain Dev 7 13ndash24
IPCC 2006 2006 IPCC Guidelines for National Greenhouse GasInventories (wwwipcc-nggipigesorjppublic2006gl)
Jaffal I Ouldboukhitine S-E and Belarbi R 2012 A comprehensivestudy of the impact of green roofs on building energyperformance Renew Energy 43 157ndash64
Jansson Aring 2013 Reaching for a sustainable resilient urban futureusing the lens of ecosystem services Ecol Econ 86 285ndash91
Khan S Cao Q Zheng Y M Huang Y Z and Zhu Y G 2008 Healthrisks of heavy metals in contaminated soils and food cropsirrigated with wastewater in Beijing China Environ Pollut152 686ndash92
Kimball B A 1983 Carbon dioxide and agricultural yield anassemblage and analysis of 430 prior observations Agron J 75779ndash88
Klein G Krebs M Hall V OrsquoBrien T and Blevins B B 2005Californiarsquos waterndashenergy relationship California EnergyCommission Report CEC-700-2005-011-SF (wwwenergycagov2005publicationsCEC-700-2005-011CEC-700-2005-011-SFPDF)
Krannich J M 2006 A modern disaster agricultural land urbangrowth and the need for a federally organized comprehensiveland use planning model Cornell J Law Public Policy 16 56ndash99
Kulak M Graves A and Chatterton J 2013 Reducing greenhouse gasemissions with urban agriculture a life cycle assessmentperspective Landsc Urban Plan 111 68ndash78
Kuswardhani N Soni P and Shivakoti G P 2013 Comparativeenergy input-output and financial analyses of greenhouse andopen field vegetables production in West Java IndonesiaEnergy 53 83ndash92
Leach G 1975 Energy and food production Food Policy 1 62ndash73Levis J W and Barlaz M a 2011 What is the most environmentally
beneficial way to treat commercial food waste Environ SciTechnol 45 7438ndash44
Loder A 2014 Therersquos a meadow outside my workplace aphenomenological exploration of aesthetics and green roofs inChicago and Toronto Landsc Urban Plan 126 94ndash106
Mamais D Noutsopoulos C Dimopoulou A Stasinakis A andLekkas T D 2015 Wastewater treatment process impact onenergy savings and greenhouse gas emissions Water SciTechnol 71 303ndash8
Martellozzo F Landry J-S Plouffe D Seufert V Rowhani P andRamankutty N 2014 Urban agriculture a global analysis of thespace constraint to meet urban vegetable demand EnvironRes Lett 9 064025
Martınez-Blanco J Munoz P Anton A and Rieradevall J 2011Assessment of tomato Mediterranean production inopen-field and standard multi-tunnel greenhouse withcompost or mineral fertilizers from an agricultural andenvironmental standpoint J Clean Prod 19 985ndash97
McClintock N Cooper J and Khandeshi S 2013 Assessing thepotential contribution of vacant land to urban vegetableproduction and consumption in Oakland California LandscUrban Plan 111 46ndash58
McCurry D Bear S Bae J Sedlak D McCarty P and Mitch W 2014Superior removal of disinfection byproduct precursors and
pharmaceuticals from wastewater in a staged anaerobicfluidized membrane bioreactor compared to activated sludgeEnviron Sci Technol Lett 1 459ndash64
Metson G Aggarwal R and Childers D L 2012 Efficiency throughproximity changes in phosphorus cycling at theurban-agricultural interface of a rapidly urbanizing desertregion J Ind Ecol 16 914ndash27
Milan C 2015 Milan Urban Food Policy Pact (wwwfoodpolicymilanoorgenurban-food-policy-pact-2)
Mohareb E A MacLean H L and Kennedy C A 2011 Greenhousegas emissions from waste managementmdashassessment ofquantification methods J Air Waste Manage Assoc 61480ndash93
Mok H-F F Williamson V G Grove J R Burry K Barker S F andHamilton A J 2013 Strawberry fields forever Urbanagriculture in developed countries a review Agron SustainDev 34 21ndash43
Moslashller J Boldrin A and Christensen T H 2009 Anaerobic digestionand digestate use accounting of greenhouse gases and globalwarming contribution Waste Manage Res 27 813ndash24
Monlau F Francavilla M Sambusiti C Antoniou N Solhy ALibutti A Zabaniotou A Barakat A and Monteleone M 2016Toward a functional integration of anaerobic digestion andpyrolysis for a sustainable resource management Comparisonbetween solid-digestate and its derived pyrochar as soilamendment Appl Energy 169 652ndash62
Mortensen L M 1987 Review CO2 enrichment in greenhousesCrop responses Sci Hortic 33 1ndash25
Mortimer N D Cormack P Elsayed M A and Horne R E 2003Evaluation of the comparative energy global warming andsocio-economic costs and benefits of biodiesel (httpsciencesearchdefragovukDefaultaspxMenu=MenuampModule=MoreampLocation=NoneampCompleted=0ampProjectID=10701)
Nicholson C F He X Gomez M I Gao H O and Hill E 2015Environmental and economic impacts of localizing foodsystems the case of dairy supply chains in the NortheasternUnited States Environ Sci Technol 49 12005ndash14
Oke T R 1973 City size and the urban heat island Atmos Environ 7769ndash79
Orsini F Gasperi D Marchetti L Piovene C Draghetti SRamazzotti S Bazzocchi G and Gianquinto G 2014 Exploringthe production capacity of rooftop gardens (RTGs) in urbanagriculture the potential impact on food and nutritionsecurity biodiversity and other ecosystem services in the cityof Bologna Food Secur 6 781ndash92
Orsini F Kahane R Nono-Womdim R and Gianquinto G 2013Urban agriculture in the developing world a review AgronSustain Dev 33 695ndash720
Pagano M A and Bowman A O 2000 Vacant land in cities an urbanresource Brookings Institute Report (wwwbrookingseduwp-contentuploads201606paganofinalpdf)
Pataki D E et al 2011 Coupling biogeochemical cycles in urbanenvironments ecosystem services green solutions andmisconceptions Front Ecol Environ 9 27ndash36
Payen S Basset-Mens C and Perret S 2015 LCA of local andimported tomato an energy and water trade-off J Clean Prod87 139ndash48
Pelletier N Audsley E Brodt S Garnett T Henriksson P Kendall AKramer K J Murphy D Nemecek T and Troell M 2011Energy intensity of agriculture and food systems Annu RevEnviron Resour 36 223ndash46
Pimentel D Williamson S Alexander C E Gonzalez-Pagan OKontak C and Mulkey S E 2008 Reducing energy inputs in theUS food system Hum Ecol 36 459ndash71
Pirog R Van Pelt T Enshayan K and Cook E 2001 Food fuel andfreeways an Iowa perspective on how far food travels fuelusage and greenhouse gas emissions Report(httplibdriastateeducgiviewcontentcgiarticle=1002ampcontext=leopold_pubspapers)
Plawecki R Pirog R Montri A and Hamm M W 2014 Comparativecarbon footprint assessment of winter lettuce production intwo climatic zones for Midwestern market Renew Agric FoodSyst 29 310ndash8
15
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
16
Environ Res Lett 12 (2017) 125004
Racoviceanu A I Karney B W Kennedy C A and Colombo A F2007 Life-cycle energy use and greenhouse gas emissionsinventory for water treatment systems J Infrastruct Syst 13261ndash70
Ramaswami A Boyer D Nagpure A S Fang A Bogra S Bakshi BCohen E and Rao-Ghorpade A 2017 An urban systemsframework to assess the trans-boundary foodndashenergyndashwaternexus implementation in Delhi India Environ Res Lett 12025008
Riva C Schievano A DrsquoImporzano G and Adani F 2014Production costs and operative margins in electric energygeneration from biogas Full-scale case studies in Italy WasteManage 34 1429ndash35
Romero-Guiza M S Peces M Astals S Benavent J Valls J andMata-Alvarez J 2014 Implementation of a prototypaloptical sorter as core of the new pre-treatmentconfiguration of a mechanical-biological treatment planttreating OFMSW through anaerobic digestion Appl Energy135 63ndash70
Saiz S Kennedy C Bass B and Pressnail K 2006 Comparative lifecycle assessment of standard and green roofs Environ SciTechnol 40 4312ndash6
Sanscartier D Maclean H L and Saville B 2012 Electricityproduction from anaerobic digestion of householdorganic waste in Ontario techno-economic and GHGemission analyses Environ Sci Technol 461233ndash42
Sanye-Mengual E Oliver-Sola J Montero J I and Rieradevall J 2015An environmental and economic life cycle assessment ofrooftop greenhouse (RTG) implementation in BarcelonaSpain Assessing new forms of urban agriculture from thegreenhouse structure to the final product level Int J Life CycleAssess 20 350ndash66
Schafft K A Jensen E B and Clare Hinrichs C 2009 Food desertsand overweight schoolchildren evidence from PennsylvaniaRural Sociol 74 153ndash77
Shiina T Hosokawa D Roy P Orikasa T Nakamura N andThammawong M 2011 Life cycle inventory analysis of leafyvegetables grown in two types of plant factories Acta Hortic919 115ndash22
Shrestha S Fonoll X Khanal S K and Raskin L 2017 Biologicalstrategies for enhanced hydrolysis of lignocellulosic biomassduring anaerobic digestion current status and futureperspectives Bioresour Technol 245 1245ndash57
Smil V 2004 Improving efficiency and reducing waste in our foodsystem Environ Sci 1 17ndash26
Smit J and Nasr J 1992 Urban agriculture for sustainable citiesusing wastes and idle land and water bodies as resourcesEnviron Urban 4 141ndash52
Smith A Brown K Ogilvie S Rushton K and Bates J 2001 Wastemanagement options and climate change final report to theEuropean Commission
Smith A Stadler L Cao L Love N Raskin L and Skerlos S 2014Navigating wastewater energy recovery strategies a life cyclecomparison of anaerobic membrane bioreactor andconventional treatment systems with anaerobic digestionEnviron Sci Technol 48 5972ndash81
Smith A Stadler L Love N Skerlos S and Raskin L 2012Perspectives on anaerobic membrane bioreactor treatment ofdomestic wastewater a critical review Bioresour Technol 122149ndash59
Specht K Siebert R Hartmann I Freisinger U B Sawicka MWerner A Thomaier S Henckel D Walk H and Dierich A2014 Urban agriculture of the future an overview ofsustainability aspects of food production in and on buildingsAgric Human Values 31 33ndash51
Tamburini E Pedrini P Marchetti M Fano E and Castaldelli G2015 Life cycle based evaluation of environmental andeconomic impacts of agricultural productions in themediterranean area Sustainability 7 2915ndash35
Taylor J R and Lovell S T 2012 Mapping public and private spacesof urban agriculture in Chicago through the analysis ofhigh-resolution aerial images in Google Earth Landsc UrbanPlan 108 57ndash70
Thebo A L Drechsel P and Lambin E F 2014 Global assessment ofurban and peri-urban agriculture irrigated and rainfedcroplands Environ Res Lett 9 114002
US Global Change Research Program 2014 Climate ChangeImpacts in the United States The Third National ClimateAssessment (nca2014globalchangegov5CnThis)
Uckun Kiran E Trzcinski A P Ng W J and Liu Y 2014Bioconversion of food waste to energy a review Fuel 134389ndash99
US Census Bureau 2015 2010 Census Urban and RuralClassification and Urban Area Criteria (wwwcensusgovgeoreferenceuaurban-rural-2010html)
US Department of Agriculture 2014 US census of agricultureNational Level Data vol 1 (wwwagcensususdagovPublications2012Full_ReportVolume_1_Chapter_1_US)
US Environmental Protection Agency 2008 Ensuring a sustainablefuture an energy management guidebook for wastewater andwater utilities Report (httpsnepisepagovExeZyPURLcgiDockey=P1003Y1GTXT)
US Environmental Protection Agency 2010 Evaluating theenvironmental impacts of packaging fresh tomatoes usinglife-cycle thinking and assessment a sustainable materialsmanagement demonstration project Report (wwwepagovwastesconservetoolsstewardshipdocstomato-packaging-assessmentpdf)
US EPA 2015 eGRID tablesmdash2012 (wwwepagovenergyegrid)US EPA 2017 Inventory of US greenhouse gas emissions and sinks
1990ndash2015 Report (Washington DC) (wwwepagovsitesproductionfiles2017-02documents2017_complete_reportpdf)
USDA ERS 2010 Energy use in the US food system Report(wwwersusdagovmedia136418err94_1_pdf)
USDA ERS 2014 Farm labor (wwwersusdagovtopicsfarm-economyfarm-labor)
USDA ERS 2013 Food Availability Data Syst (wwwersusdagovdata-productsfood-availability-(per-capita)-data-systemaspx)
Vitiello D and Brinkley C 2013 The hidden history of food systemplanning J Plan Hist 13 91ndash112
Wakefield S Yeudall F Taron C Reynolds J and Skinner A 2007Growing urban health community gardening in South-EastToronto Health Promot Int 22 92ndash101
Ward J D 2015 Can urban agriculture usefully improve foodresilience Insights from a linear programming approach JEnviron Stud Sci 5 699ndash711
Webb J Williams A G Hope E Evans D and Moorhouse E 2013Do foods imported into the UK have a greater environmentalimpact than the same foods produced within the UK Int JLife Cycle Assess 18 1325ndash43
Weber C L and Matthews H S 2008 Food-miles and the relativeclimate impacts of food choices in the United States EnvironSci Technol 42 3508ndash13
West T O and Marland G 2002 A synthesis of carbon sequestrationcarbon emissions and net carbon flux in agriculturecomparing tillage practices in the United States Agric EcosystEnviron 91 217ndash32
Williams H and Wikstrom F 2011 Environmental impact ofpackaging and food losses in a life cycle perspective acomparative analysis of five food items J Clean Prod 19 43ndash8
World Health Organization 2006 Guidelines for the safe use ofwastewater excreta and greywater Report vol 1 (GenevaWHO) (httpwhqlibdocwhointpublications20069241546832_engpdf)
Zhang S Bi X T and Clift R 2013 A life cycle assessment ofintegrated dairy farm-greenhouse systems in British ColumbiaBioresour Technol 150 496ndash505
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