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Renewable Energy 71 (2014) 156e165
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Renewable Energy
journal homepage: www.elsevier .com/locate/renene
Low cost tubular digesters as appropriate technology for widespreadapplication: Results and lessons learned from Bolivia
Jaime Martí-Herrero a, *, Maria Chipana b, Carlos Cuevas b, Gabriel Paco c, Victor Serrano d,Bernhard Zymla e, Klas Heising e, Jaime Sologuren b, Alba Gamarra f
a Centre Internacional de M�etodes Num�erics en Enginyeria (CIMNE), Building Energy and Environment Group, Edifici GAIA (TR14), C/Rambla SantNebridi 22, 08222 Terrassa, Barcelona, Spainb Energising Development Bolivia (EnDev-Bolivia/GIZ), Boliviac Universidad Catolica Boliviana, Unidad Acad�emica Campesina CarmenPampa, Boliviad Comunidad Collpapampa Tiquipaya, Boliviae Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ), Germanyf Centro de Informaci�on Nacional de Energías Renovables (CINER), Bolivia
a r t i c l e i n f o
Article history:Received 27 May 2013Accepted 16 May 2014Available online
Keywords:Household low cost tubular digesterBiogas programmeBiogasBio-slurryBoliviaAppropriate technology
* Corresponding author. Tel.: þ34 937398575; fax:E-mail addresses: [email protected]
(J. Martí-Herrero).
http://dx.doi.org/10.1016/j.renene.2014.05.0360960-1481/© 2014 Elsevier Ltd. All rights reserved.
a b s t r a c t
This paper presents the results and lessons learned from four and a half years of implementing low costtubular digesters in Bolivia. The selection of this technology is justified in comparison with other populartechnologies such as fixed dome or floating drum digesters. The highlighted weakness of the tubularmodel (its short life expectancy), is transformed into a strength, making the low cost tubular digester anappropriate technology for widespread application. The experiences in Bolivia show that the success ofbiogas programs depend more on socio-economic factors than on the validated technology selected,suggesting that local circumstances are a critical, and often underestimated, factor to be taken intoconsideration in the praxis. Finally, some testimonies of the use of biol (bio-slurry or effluent) are re-ported, identifying the high potential of this anaerobic digestion product that provides a food sovereigntyapproach, reduced expansion of the agricultural frontier, increased agricultural productivity and hencefamily income, that other household energizing systems do not have. A brief report of lessons learned isalso included.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
One of the indicators for energy poverty at the household level isthe reliance on traditional use of biomass for cooking. Another in-dicator is the lack of access to electricity. The International EnergyAgency (IEA) reported in 2012, that 2.6 billion did not have access toclean cooking facilities and nearly 1.3 billion people continuewithout access to electricity in the world [1].
The IEA [2] has proposed a case for achieving universal modernenergy access: by providing access to clean cooking facilities wherethese are lacking. The IEA proposal aims to achieve this goal bymeeting the following targets within this proportion: 55% ofimproved cook stoves,15% of biogas systems and 35%with access toLiquid Petroleum Gas (LPG) stoves.
þ34 937883110., [email protected]
In order to reduce the number of households suffering energypoverty, several initiatives have been developed in local, nationaland international consortiums. One of these initiatives is theEnergising Development Program (EnDev) that promotes the sup-ply of modern energy technologies and improved (more efficient)cooking stoves to household and small-scale businesses. EnDevstarted in 2005, as a partnership between the Netherlands, Ger-many, Norway, Australia, the United Kingdom and Switzerland, andcooperates with more than 20 countries in Africa, Latin Americaand Asia. The Deutsche Gesellschaft für Internationale Zusamme-narbeit (GIZ) is acting as the lead agency for implementing thisProgram in Bolivia.
Biogas systems are considered as an appropriate technology byEnDev, with a relatively small implementation target whencompared to the total number of the initiatives, in line with the IEAproposal proportions described above. A digester has several im-pacts on the daily routine of small farmers. These include the use ofbiogas for cooking instead of solid biomass (wood, charcoal, cropresidues or dry dung) as combustible, resulting in a healthier,
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smoke-free indoor ambient when cooking [3,4]; reducing thepressure on local biomass resources and also reducing the timededicated (mainly by women and children) to collecting biomassfuel. In addition, the production of bio-slurry or effluent (known asBiol in Latin America and the Caribbean region) and its utilizationas an organic fertilizer has shown a great potential to increase thecrop production and therefore the farmers' income, as commentedfurther on in this document.
The digesters offer advantages over other forms of wastetreatment. These are summarized below from the benefits reportedand referenced by Ward [5] and Yiridoe [6].
� Less biomass sludge is produced in comparison to aerobictreatment technologies, reducing the chemical oxygen demandby 60e90% and the biochemical oxygen demand by up to 80%.
� Significant removal (up to 98%) of coliforms and other patho-gens. This is especially true for multi-stage digesters or if apasteurization step is included in the process.
� Reduced water contamination, improved manure managementand use and reduced eutrophication.
� Minimal odourous emissions as 99% of volatile compounds areoxidatively decomposed upon combustion, e.g. H2S forms SO2.
� The slurry produced (digestate, effluent, biol) is an improvedfertilizer both in terms of its availability to plants and itsrheology. It also reduces weed seed germination.�A source of carbon neutral energy is produced in the form ofbiogas.
� GHC emission reduction by a factor of 21 due to conversion ofCH4 to CO2.
The biogas EnDev-Bolivia program activities began in 2007 withsmall pilot projects and some workshops until mid 2012, whenthese activities stopped due financial resource depletion and theconcentration of the remaining resources primarily on providingimproved cooking stoves. Also, it was felt that both the technologydevelopment and the implementation strategies had been taken tosufficient maturity for other actors but EnDev to pick up thedissemination.
This paper documents the Endev experiences on the promotionof low cost digesters in Bolivia. The paper presents the context ofBolivia, the selection of the tubular low cost digester as the accuratetechnology to be promoted, the results of activities of four and ahalf years and the economical, technical and socio-cultural lessonslearned.
2. Biogas in Bolivia context
2.1. First projects, first failures
Bolivia, like other Latin American countries, first introducedbiogas systems in the 1980s. The technology selected was the fixed-dome (BORDA model) digester, which was very well known inAsian countries. 65 household digesters were implemented be-tween 1986 and 1992. A few years later, none of the 65 digesterswere working and no replication followed. The high level of sub-sidy, poor selection of users and lack of post-installation technicalassistance are the most important contributory factors to thissubstantial project failure. A very similar, and equally unsuccessful,experience happened in Cajamarca (Peru) around the same time.Lessons learned from the Peruvian case can be extrapolated toBolivia from the Spagnoletta report in 2007 [7].
Between 1992 and 2002, no new digester installations werereported. In 2002, 23 low cost tubular digesters where imple-mented in Mizque, at an altitude of 2400 m above sea level(m.a.s.l.). In 2003, the first digester working over 4000 m.a.s.l. was
reported by Martí-Herrero [8]. Between 2002 and 2006 severalsmall tubular digesters were installed, mainly in Cochabamba(valley, warm climate) and La Paz (altiplano, cold climate). Theimplementation scheme was similar to that employed in the 1980swith the fixed-dome digester, resulting in less than 25% technologyappropriation by the users.
Bolivia is a country with a broad history of aid projects for ruraldevelopment. In the time period from 1991 to 2005, Bolivia was thecountry that received most aid funds annually in Latin America. Interms of aid funding per habitant, Bolivia is still the country(excepting Guyana and Suriname) that receives the most aid: $67US per habitant in 2010 [9]. These circumstances help explain thehigh subsidies given to the users to access a digester. Due to thewelfare schemes of many of the projects and demands, users wereused to receiving a certain amount of financial support. The otherissue, low levels of technical assistance and follow up of the users,can also be explained by the particular characteristics of Bolivia.With an area of 1,050,000 Km2 and roughly 11 million inhabitants,it is the country (excepting Guyana and Suriname) with the lowestpopulation density in Latin America (9.5 hab/km2). Also, theecological diversity, with three distinct regions, is very significant.The three main regions are: the altiplano which is around3500e4500 m.a.s.l and has mainly a cold climate; the valleys from1500 to 3500 m.a.s.l. with warm climate, and the tropics from 300to 1500 m.a.s.l. (tropical weather). This variety is compounded bycultural diversity: 67% of the total population is indigenous and ismade up of 38 distinct and officially recognized indigenous nations.The combination of all these aspects make technical assistanceparticularly difficult and expensive due to the dispersion of users,the inadequacy of the road infrastructure in rural areas (notablyduring the rainy season), and also due to the cultural differencesbetween users.
With this experience, very similar to those in other LatinAmerican countries, it can be deduced, and it has been validated,that the failure of these initiatives has been a result of the strategyused in the projects, rather than because of the technologyinvolved, (fixed dome or low cost tubular in the Bolivian case).
2.2. Situation before Endev-Bolivia
In Bolivia there was only one NGO implementing digesters forthe whole country in 2007, with no technology transfer either tothe users or to other institutions. The biogas technology was un-known to the great majority of the farmers, and in some high po-tential areas the technology had a very low credibility due toconstant project failure. Since 1986, all the projects had focused onthe benefit of biogas as a fuel for cooking, with the use of biol as asecondary or collateral product from the anaerobic digestion.
EnDev-Bolivia came in and focused on technology transfer tonew institutions (NGOs, municipalities and farmers), consolidationof the technology (design methodology, design adaptation todifferent climatic regions, biogas reservoirs, etc.), low direct sub-sidies to the farmers, relatively high levels of investment in tech-nical assistance and follow-up of users.
3. Biogas technology selection
The introduction of a biogas system in the rural area of Bolivianeeds to consider the dispersion of the rural population, inade-quate roads in the rainy season, long distances, high poverty and acontinuous migration of rural labor to the cities. Under these cir-cumstances, low-cost digesters offer significant advantages; char-acterized by the absence of active heat or mixing devices. Thisreduces the economic investment required and also minimizes thecomplexity of operation and maintenance. Fixed-dome, floating
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drum and tubular digesters (also known as flexible bag), balloondigesters, tube digesters or plastic tubular digesters are allconsidered low-cost models.
The fixed-dome digesters are the most popular model as shownby the National biogas Programs of South Asia [10], India [11] andChina [12] where more than 45 million units have been imple-mented. It is recognized as a robust technology. For its construction,bricks cement, sand and iron all need to be transported to the ruralcommunities. Also, a skilled mason is needed to ensure the correctconstruction of the dome to avoid leakages. This all increases theoverall cost. This technology could be adequate for systemsinstalled near the cities or rural areas with low transport costs, butrather not for dispersed, poor, partially isolated rural communities.The analysis for floating drum digesters is similar to that of thefixed-dome. These models are famous because of their long-life,which can exceed 20 years, justifying the high investmentinvolved. They could be interesting for dairy cattle or pig famersthat have already invested in infrastructure and have a long-termeconomic horizon (more than five years). However, they do notseem adequate for poor farmers whose investment horizon is lessthan two years and who often change agricultural activities forothers like: selling the cattle and farmland/or migrating to cities.
The household low cost tubular digesters were developed byPreston and co-workers [13,14] as a cheaper model than theTaiwanese ‘red mud’ [15]. Vietnam is particularly relevant withinAsia with about 20,000 units installed by 2006 [16]. Some LatinAmerican countries like Mexico, Nicaragua, Colombia, Costa Rica[17], Peru [18] and Bolivia [19,20] are the ones where this low costtechnology is being implemented, developed and adapted to coldclimate regions despite only making use of natural solar heating[19,21]. Compared to fixed-dome digesters, in terms of materialsand labor, this technology costs half of what fixed-dome digesterscost. Despite the fact that the estimated average life expectancy ofthe tubular digester is lower (5 years) there are some examples ofdigesters in Cochabamba that are 10 years old and are still working,many others have prevailed over 5 years, but the strategy ofimplementation is more related to the duration of the systems than
Fig. 1. Schematic design and dimensions for a low cost tubular digester standardized for theto improve thermal performance of the system.
with the lifespan of materials, as mentioned above. The trans-portation of the material needed for tubular digesters is easier andcheaper (all thematerials can be carried bya donkey) and thusmoreappropriate for poor farmers living in remote rural areas. Because ofthese considerations, the low-cost tubular digesters are a technol-ogy with great potential for knowledge transfer from farmer tofarmer [8] (Fig. 5.2). In accordance to these factors the low-costtubular digesters (Fig. 1) were the logical choice for the EnDevsupport of digesters in Bolivia focused on the small scale farmers.
Garfi et al., in 2014 [22] compares the fixed dome digestermodelwith the tubular one, giving a range of biogas production rate (inhigh altitude conditions) for the first ones of 0.35e0.7 m3/m3/d and0.09e0.47 m3/m3/d for the second ones, being the location, feed-stock composition and operational parameters (i.e. HRT, OLR) theway to explain the differences for each model. It is remarkable thatfixed dome digesters can be fed with a ratio manure:water 1:1,while tubular ones 1:3. This means that for the same amount offresh manure to load, the tubular digester should have a doubleamount of liquid volume than the fixed dome, but the biogas bell ofthe fixed dome occupies 25% of the total volume, while the tubulardigester only occupies 20%. This is necessary to consider whencomparing the cost of both systems.
A recent study from Bolivia (2013) [23] reports that a fixed domedigester of 6 m3 total volume costs 1004 us$ and an equivalent11.3 m3 tubular one costs 503 us$, hand labor included in both casesand a protection greenhouse in the second one. As the fixed domedigester has a 20 years lifespan and the plastic tubular only 5, thetotal cost over 20 years for this model is 1088 us$, considering thatthe greenhouse and the tubular plastic are replaced three timesafter installation along 20 years (labor hand is included). At last,due to a minor economic investment, low cost tubular digesters cancover an economic-social gap that other models do not.
In conclusion, all the biogas technologies have advantages anddisadvantages. The right technological choice ultimately dependson the local factors (social, technical, economical), and the partic-ular objective and subjective circumstances of each farmer: 1.objective such as investment capacity or availability of manure and
altiplano region. In this cold climate, a greenhouse and trench insulation must be added
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water, and 2. subjective such as motivation or social recognition.The final decision must be taken by the farmer after having accessto clear information about each of the technologies available intheir environment.
4. The low-cost tubular digesters technology
The reactor tank is made with a double tubular polyethyleneplastic layer, each with a thickness usually in the range0.15e0.3 mm. The dimensions of the tank depend on the plasticavailable, and can vary from 3 to 8 m in circumference. A detaileddesign methodology can be found in [20]. The inlet and outlet isdone with 400 or 600 PVC pipes that are tied with rubber, car wheel,inner tubes to the tubular plastic. This tank is half-buried in order tokeep all the liquid phase inside the trench (Fig. 2.1). The gas phaseat the top forms a biogas bell, from where the biogas is extracted,with a water pipe, usually to the kitchen for cooking. There is awater trap relief valve to allow the excess biogas, that which isproduced and not consumed, to escape. The biogas is conductedfrom the digester to two or three vertical plastic reservoirs, thatused to be made of tubular polyethylene plastic (Fig. 2.3), and noware made with heat sealed rubber canvas that have a longer life-span. These reservoirs have a set of checks which increase thepressure when cooking. Between the reservoir and the biogasstove, a simple in-line H2S filter is installed by introducing ironwool inside the pipe (Fig. 2.4). The household digester is fed everyday with 20 kg of fresh manure and 60 L of water, producing
Fig. 2. Clockwaise order from top left: 1. tubular digester for tropical region (Santa Cruz);vertical biogas reservoirs in Viloma (Cochamaba); 4. biogas cook stove at an aimara indige
0.7e0.8 m3 of biogas per day and 80 L of biol (Fig. 2.2). These figuresare independent of the climatic region, as for each climate a stan-dard design is given to achieve the same results [24]. In cold cli-mates, such as in the altiplano (Fig. 3), the tubular digester isinsulated from the ground and integrated into a greenhouse, whichis composed of thermally massive adobe walls and covered with atransparent plastic sheet. Adobewalls store heat during the day andrelease it at night [21].
The maintenance needed involves: keeping enough water in thewater trap, replacing the wire wool when odor is detected from thebiogas when cooking, and purging any water that may havecondensed in the biogas pipes.
The material cost of a typical household digester is around $220to $280 (USD) depending on the climatic region: in colder climatesthe digester needs to be bigger and it is integrated into a green-house. The total labor costs are $100 (US); 75% for the installationand 25% for digging. The trench can be done by the family, thusreducing the financial cost by 25%.
The relevance of this technology is increasing and more scien-tific publications at indexed journals have been published in recentyears. Since the low cost digesters have no active heating devices,the local climate dictates the main difference in results. The lowpressure at high altitudes is not a major influence on results asreported by Alvarez et al. [25].
Langsing et al. [17,26e28] reported results of low cost tubulardigesters in the tropical warm climate of Costa Rica. Ferrer et al.
2. foliar application of biol (Bio-slurry) over potato crops in the altiplano (La Paz); 3.nous house in Viacha (La Paz).
Fig. 3. Left, cold climate tubular digester as llama slaughterhouse waste treatment system in the altiplano region of Tarija. Right, interior view of the greenhouse of a cold climatetubular digester in Viacha (La Paz).
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[29] reported the results of monitoring a digester at the sea coastwarm climate of Lima (Peru).
For cold climate anaerobic digestion there have been, until now,two types of reports: those that show the results of laboratory scaledigesters in simulated cold climate conditions that work withdifferent typical substrates of the cold climate regions like; cow,llama (Andean camelid species, Lama guanicoe glama) and sheepmanure from Alvarez et al. [25,30e32]; and those that report re-sults from real scale low cost tubular digesters in cold climateconditions in Peru from Ferrer et al. [18], Perrigault et al. [21], anGrafi et al. [33e36] and Bolivia from Martí-Herrero [19,20].
Table 1Type of final digester user.
Families 740Schools 2Community centers 5
5. EnDev biogas project strategy
The promotion of digesters beganwith small scale pilot projectsaccompanied by a 3 day workshop in 2007. This experience led to a“democratization” of the technology among farmers and in-stitutions [8] from 2008 onwards. The key ideas for these projectswere:
� Standardization of the household digesters as a result ofdifferent climate regions (tropic, valleys and Altiplano) [24]
� Dissemination of digester technology directly to farmers, withclear information about benefits (biol and biogas), nonmarket cobenefits, costs, operation and maintenance, care requirements,and weaknesses of the technology
� Subsidy for installation, technical assistance, follow up, and 25%of the material cost of the digester
� Workshops and seminars for NGOs and technicians withtraining of: installation, design and project development
� Focus on biol and biogas as the main benefits with the sameimportance.
The projects could be realized by EnDev directly with thefarmers or by a local institution, however in this case no travel,salaries or indirect cost would be transferred to the local in-stitutions, in order to avoid provoking a fashion for digesters in theNGOs. The aim was to try to integrate the digesters in normaldevelopment projects that NGOs were executing with otherfinancial support. In this way, the digesters should become a newtool to be incorporated in existing development projects.
In order to generate a sustainable sector, in 2009 a researchinfrastructure with international and local actors such as univer-sities and NGOs was founded. The “laboratory” in Viacha (La Paz),should link high quality research in digesters, biogas and biol withthe local requirements of farmers and industrial processes.
6. Results
After four and a half years, from early 2007 to mid. 2012, 747digesters were installed in Bolivia. Most of them, 740, are house-hold digesters, 2 have been installed in schools, and 5 in commu-nity centers as can be seen in Table 1. These results are coherentwith the objectives of the project: to promote small scale digestersand to respond to promotion, research and development logic.
Most of the digesters have been installed in the warm valleysregion (48.6%), followed by the cold altiplano region (38.3%) andthen the tropical area (13.1%), as shown in Table 2. The type offeedstock used for the digesters (Table 3) is dominated by dairycattle (87%) followed by pig manure (11.5%) and just a testimonialnumber of poultry, sheep or rare substrates such as llama manure.Also, for research and development purposes, one digester hasbeen implemented as a waste water treatment system for 400people, and two more systems for the treatment of llama and cowslaughterhouse waste (Fig. 3 left, and Fig. 5.4).
The regional distribution is not in relation to the technical po-tential of the digesters, as in each region there are a similar numberof small farmers. Instead it is related to the presence of NGOs. Theseare concentrated in the valleys and altiplano where poverty ratesare higher. The high numbers of digesters for valleys are due to analliance made with a government rural development program inthat region during the EnDev biogas activities. The preference forcow substrate as feedstock for the digester is due to the fact that, inBolivia, the small farmer tends to have a very poor infrastructurewith, for example, stables without a cement floor. This implies thatthe manure must be collected and fed to the digester by hand. Inthese conditions, it is easier to introduce the daily digester feedingroutine in dairy cattle management procedures, as the farmers havetheir fixed time table of activities every day, and the hand man-agement of cow manure is culturally more acceptable than forother types of manures such as from pig or chicken. Also, pig farmstend to be medium or large scale. In contrast, dairy farms aretypically small scale and thus better aligned with the projects'focus. The low numbers of digesters fed with llama manure are dueto the fact that there was no previous experience with this sub-strate: validation was required and has now been achieved.
The alliances with institutions have been mainly with theaforementioned rural development programs in the valleys (44.4%),
Table 2Distribution of digesters by climate region.
Climate region Number of plants % Of total
Altiplano 286 38.3%Valley 363 48.6%Tropic 98 13.1%Total 747
Fig. 4. Main research infrastructure of the CIB3, with 10 experimental tubular digestersoperated and monitored in real weather conditions at 3850 m.a.s.l (Viacha, La Paz).
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followed by NGOs (28.9%), directly with the farmers (16.3%), mu-nicipalities (9.1%) and department governments (1.2%), as can beseen in Table 4. In the case of the government development project,it can be considered the same as working directly with farmers asthe farmers' associations received governmental funds and imple-mented the project on their own, following a series of standardizedsteps. Consequently 60.7% of the projects have been executeddirectly with the farmers. This reflects the empowerment of theBolivian rural population and their ability to make decisions andimplement their own development projects without the assistanceof NGOs. In some cases the NGOs are perceived as an unnecessaryactor. This, again, is related to the huge amount of aid funds thatimply a multiplication of the number of NGOs that do not alwayshave the capacity or ability to work efficiently. Finally, the farmerstend to trust only historical NGOs with high credibility and newones that either earn credibility or happen to be recommended bythe historical ones.
6.1. Other results
The creation of the Research Center for Digesters, Biogas andBiol (CIB3 for its acronym in Spanish) in the altiplano of Bolivia, hasbeen one of the main goals achieved in terms of assuring the sus-tainability of the biogas EnDev-Bolivia impacts, after conclusion ofthe program itself. The main strength of the CIB3 is the multidis-ciplinary research consortium that coordinates activities. Theseinclude the alliance with historical rural development NGOs(Centro de Investigaci�on y Promoci�on del Campesinado, CIPCA) thataims to have permanent contact with farmers, know their needsand transfer the knowledge generated; the association with sus-tainable technology NGOs (Centro de Promoci�on de TecnologíasSostenibles, CPTS) that focusses on semi-industrial process such ascoffee benefit, slaughterhouses, etc; the public university of La Paz(UniversidadMayor de San Andres, UMSA) with the departments ofChemistry Engineering (Instituto de Investigaci�on de ProcesosQuímicos, IIDEPROQ) and Agronomy (Instituto de Investigaci�on deRecursos Naturales, IIAREN), and the collaboration of a Spanishpublic research institution (Centre Internacional de M�etodesNum�erics en Enginyeria, CIMNE).
The CIB3 has 10 low cost tubular digesters that operate in realcold weather conditions at 3850 m.a.s.l. where different substrates,retention time and co-digestion parameters are monitored (Fig. 4).The objective is not only to improve the biogas production, but alsoto obtain better quality biol, and to research the proper dosage and
Table 3Distribution of type of substrate used to feed the digesters.
Type of substrate Number of plants % Of total
Cow 650 87.0%Pig 86 11.5%Llama 4 0.5%Sheep 1 0.1%Chicken 2 0.3%Waste water treatment 1 0.1%Slaughterhouse 3 0.4%Total 747
frequency of application of this fertilizer on different crop planta-tions (one of the fundamental objectives of the laboratory). To date,three papers have been published about the work realized at CIB3[19e21]. More data has been collected and will soon be published.The CIB3 is also carrying out experiments with different models ofdigesters and liquid waste treatment.
This research infrastructure permits validation of biogas tech-nologies from other countries in the specific cold climate and highaltitude of the Bolivian altiplano. Also, the CIB3 gives credibility tothe anaerobic digestion system in Bolivia, and allows innovationand local development of technology and human resources. Thisresearch tool, the CIB3, enables the immobility of the technology,observed in various national biogas programs of Asia and Africa [10]with only one technology certificated to be implemented, theModified CAMARTEC model, to be overcome. The CIB3 permits theintroduction of a range of validated anaerobic digestion technolo-gies that can fit better to the different types of farmers, as it will becommented below.
7. Lessons learned
7.1. Economic
7.1.1. The cost of a digesterRight from the start, let farmers know the complete cost of the
digester as a complete pack: including not only the material cost ofthe system itself, but also the costs of installation labor, protectionmaterials, and follow up or guarantee services.
7.1.2. The subsidiesReduce subsidies to that amount of money needed to make the
technology accessible to the poorest users, considering their realcapacity of investment, in order tominimize the distortion of a puremarket based scheme of implementation. High subsidies implyhigher failure rates in terms of appropriation of the technology bythe user: higher construction/installation ratesmay be achieved butsustainability rates are lower [12]. Demonstrative digesters shouldbe subsidizedwith the same idea: justwith theminimumamount ofmoney required to overcome the barrier of unfamiliarity with thetechnology. As Mwirigi et al. [37] reports from Kenya, the socio-economic status of the farmer affects the decision to adopt thetechnology but does not affect the sustainability of the constructedplant. Therefore it can be concluded that the optimal subsidy is thatwhich overcomes economic access barriers, ensuring that the in-vestment is not prohibitive for those in poverty, yet does not distortthe market by making the systems so cheap to the farmers' under-value them and fail to take responsibility for them.
7.1.3. Credit and financial servicesIn many reports [10] credit disposal is identified as a key factor
for success, but micro-credits tend to have high rates of interest
Fig. 5. Clockwise order from top left. 1. Tubular digester prepared to be installed in Tohuaco (La Paz); 2. tubular digester being installed during a workshop in Viloma (Cochabamba).3. The highest digester working reported in 2007 at 4223 m.a.s.l. in Pakuani (La Paz). 4. A three tubular digesters in series, as a pilot plant for treating slaughterhouse fluids bearingwastes (Cochabamba), as part of the activities of CIB3.
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(12e20% annually) and not many farmers can access them becauseof guarantee considerations and lack of rural offices. In Bolivia thereare others ways of micro-financing that are already working fordairy farmers. The regional or local farmers' association asks for acommercial credit, and re-issues it in small amounts to associatedfarmers at commercial rates (6e10%), the association has a mech-anism to ensure repayment as it can retain the milk payments fromthe milk companies to the farmers.
7.2. Social
7.2.1. Clear, complete and honest informationGive clear and contrastable information about the digesters
giving equal emphasis to benefits, weakness and the workloadinvolved in operation and maintenance (biogas, biol, cookingwithout smoke, waste treatment, less pressure over the environ-ment, daily operation, maintenance activities, overall cost and carerequirements). Show failure cases and explain them in detail.
7.2.2. Local technicians, guarantee and follow upLocal technicians are the ones that install digesters, they guar-
antee the installation until the digester is working, until the userunderstands the system and its maintenance (usually 6 months),and is also able to attend doubts, repairs and substitution of oldmaterial (as the plastic tank or the greenhouse) in a local-regionalscale. These monitoring activities should be considered in the totaldigester cost. If there is no NBP in a country, it is difficult for in-stallers to live exclusively upon this activity, but it would mean an
Table 4Distribution of type of partners on digesters implementation projects.
Type of partners Number of plants % Of total
NGOs 216 28.9%Local government 68 9.1%Regional government 9 1.2%National Government 332 44.4%Farmers 122 16.3%Total 747
extra cash income to their daily tasks. In the case of an NBP microand medium enterprises could be formed more easily. These in-stallers must be certified, perhaps through the same organism thatdoes the research and development of digesters. Technicianstraining could be formal or informal, taking advantage of knowl-edge transfer from farmer to farmer capacities [8], in so far asknowledge is certified afterward. It is recommended that localtechnicians are independent from the institution that promotes thedigesters to guarantee the sustainability of this service, indepen-dently of projects time period.
7.2.3. Fixed goals of the projectsAvoid taking an overambitious and fixed number of digesters, to
be implemented in a defined period of time or region, as the mainindicator of success. This puts pressure on the implementinginstitution and on the potential and can be counterproductive. Thekeys to working successfully with real farmers are access to clearinformation, and time. Sufficient time to allow two, three, four ormore phase of the project if necessary so that the farmers can getinvolved in the project when they are ready; when they feelcomfortable rather thanwhen the project wants. “Allow some timefor the farmers to 'digest' the biodigesters technology is essential”[38].
7.2.4. Integration with family and farmThe digester must be integrated in the family's way of life
considering the best location, theway it is going to be fed, the use ofthe biol, etc. Also, the digester must be integrated in the productionprocess, becoming sustainable, displacing chemical fertilizers, andleading the farmer to a sustainable way of production with lessexpenditure. A good point is the availability of pens with concretefloor connected to the digester, as it facilitates handling and ensuresgreater appropriation and use of long-term technology.
7.2.5. Social structuresLeverage existing social structures (local, regional and national
associations of famers, local community structures, associations ofecological farmers, etc.), as they already have their own way of
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meetings and internal communication. It is necessary to knowthese social structures, understand and respect their dynamics, andavoid creating new artificial ones that alter their daily living.
7.2.6. Communal digestersSocial management of a communal digester (one digester for
more than two families) is only recommended in communities withprevious experience of communal management of other technol-ogies or tools. This also applies for digesters in schools orcommunal infrastructure.
7.3. Technical
7.3.1. Quality and appropriate technologyConsider only proven, validated technology; do not test technol-
ogies with farmers, unless they are informed and agree. Fixed-dome,floating drumor tubular digesters are validated as appropriate biogastechnologies and there is enough information about them. The choicebetween one technology or another depends on the type of farmer,climate, availability of land, water, investment cost, cheap trans-portation, accessibility, etc. Probably all technologies are suitable, butone will be more suitable than the others in each specific case.Regardless of the technology that is selected, thequalityof the systemmust be certified after the start-up of the digester.
7.3.2. Biogas and biol focusThe funding or implementing institution may have its own
motivation to focus on biogas. Such motivations include health is-sues (e.g. reducing the incidence of respiratory diseases in womencooking with firewood), or energy poverty reduction issues,appropriate treatment and management of farm waste or thepromotion of more sustainable agriculture. Ultimately the pro-ducers will be the ones to decide in which product they want tofocus. It may be the biol, the biogas, or both, and need not neces-sarily coincide with the interests of the sponsoring institution. Thefarmers need to be able to decide the approach that suits them bestaccording to their needs.
7.4. Management
7.4.1. Synergies with other projectsThe digester system involves many aspects such as energy
(biogas), environment (less deforestation and waste treatment),health (no smoke), production (biol) and gender (reduced work-load onwomen collecting firewood). Therefore, it transforms into atool that can be integrated into many different projects such aswaste and watershed management, ecology, energy, organic foodsovereignty, health, climate change mitigation and adaptation, etc.Digester projects work best if they are an additional tool of a pro-gram rather than a project in itself. Other synergies of interest arethose related to the production cycle. Huang et al. [39] identifies the“pig-biogas-fruit” or the “four in one” (with pig breeding-biogas-vegetable planting-greenhouse). These kinds of synergies can befound in the milk cycle with the patter “biol-more alfalfa-moremilk-more income” and “biogasesanitize milking tools”. Anothercycle is related to llama cattle and quinoa (Chenopodium quinoa)crops “biol-quinoa” due to the poor altiplano soil where quinoagrows.
7.4.2. CalendarSome projects come with very tight timelines, which impose
external calendars on the reality of families. A very typical caseinvolves having to run a project from its approval date and with aspecific duration, with no consideration of the agricultural calen-dar, climate conditions (rainy and dry season), or national and local
holidays. This is an error: to be successful projects must adapt to thefarmers' calendar and activities, not the other way round.
7.4.3. Research and developmentPromote the creation of a research and development tool (with
universities and NGOs, as the CIB3 laboratory) linked to the realityof digester users, in order to provide answers to farmers, localtechnicians and organism involved in digesters. This is a key fordigesters sector sustainability after projects are finished.
7.4.4. Promoter institutionAssign most of the tasks in reliable partners, looking for syn-
ergies and sustainability. It should control the diffusion and contentof the information of the technology, the subsidies, quality of in-stallers, installations and ensure a good monitoring, evaluation andtechnical assistance activities afterward.
7.5. Weaknesses and opportunities for the low cost tubular digestertechnology
The main factor for a successful introduction of digesters tosmall scale farmers, to reduce energy poverty and increase sus-tainable farming, is the implementation strategy. Assuming that avalidated technology is being used, this is more important than themodel of digester implemented. Many programs have beenimplemented to create a sustainable biogas sector [10e12], basedon fixed dome or floating drum digesters. This is highlighted as oneof the main strengths of the 20 year duration of these systems. Incontrast, the 'doubtful' life expectancy of the tubular digester hasbeen highlighted as a weakness of this technology [40,41]. Morerecently a report from Uganda, stated that this model “is unpopularbecause it has a much shorter lifespan than the other types” [42].However, this shorter lifespan, of 5 years becomes a strength of thetechnology when considered together with the lower costs ofimplementation, making it more accessible and appropriate forthose impoverished producers with an uncertain future in theirfarming activities or place of residence (urban migration). A tech-nology with 20 year lifespan and associated investment plan isneither appropriate nor attractive to a farmer that does not knowwhere he is going to be three years' time.
Another uncertainty is the fragility of the technology due to theflexible plastic employed for the tank. This can easily be solved byincluding in the cost of the digester the appropriate protection. Incold climates it is ensured by a greenhouse, and in warm andtropical areas with roof and edge walls. Protection devices shouldbe incorporated to the design and cost for all climate regions.
7.6. Biol (effluent, bio-slurry) as the great opportunity
Most of the papers that evaluate low cost digesters, indepen-dently of the country or region involved, focus on the biogas benefitas a renewable energy, and its incidence on energy povertyreduction. Examples include China [12], Kenya [37], Uganda [42],Asia and Africa [10], developing world [11]. Only in the Ghanaiancase [43] the use of the effluent (bio slurry or biol) as fertilizer isconsidered the primary benefit of low cost digesters. Likewise, onlyone report about biol produced by a low cost digesters has beenfound, corresponding to Garfi et al. [33].
In Bolivia the biol is becoming the most important product ofthe anaerobic digestion. Although more studies are needed, thefirst results from field experiments show increments of 33%e50% inproductivity of the crops in studies realized with Tobacco, Nicotianatabacum; Alfalfa, Medicago sativa; Barley, Hordeum vulgare. Thereis an upcoming paper on this subject. Also, the farmers report agreat capacity of the biol to protect the crops from freezing.
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Without foliar biol application the loss of plants can reach 80%.With biol application these losses are much lower, only reaching20e30%, (phenomena described for quinoa and potato, Solanumtuberosum). This effect is corroborated by testimonies from farmerswho say that the plants recover faster from the damages caused byfrost, after foliar application of biol (quinoa, potato and onion,Allium cepa). These reports must be validated by experiments inthe future.
8. Conclusions
The digesters have been identified as a technology that can helpin the reduction of energy poverty (biogas), and increase the sus-tainable farming (biol). Fixed-dome and floating-drum models aremore popular, but new designs based on tubular digesters are nowbecoming implemented in more significant numbers in LatinAmerica and Vietnam. The success of biogas projects does notdepend on the validated technology implemented, but on thesocial-technical and economical strategy for implementation.Tubular digesters have been seen as a short term life technology,but thanks to their lower cost, this can be a strength whenworkingwith impoverished farmers with a very short economical horizon.Low cost tubular digesters have not been considered a massiveanaerobic digestion technology, but experiences like this in Bolivia,and older ones such as the Vietnam one, position this model as avalidated tool that can fit better with some of the poorest farmers.To offer a range of technologies, and offer incentives to research anddevelopment of these digesters, it seems to be important to rein-force the democratization of the digester in the world.
Several initiatives are being carried out to democratize thistechnology, based on common aspects as market scheme, smallsubsidies, credit access and technical assistant post-installation,quality control, etc. But many other local factors should beconsidered in order to adapt these programs to the conditions ofeach country or region. These factors include social structures andthe farmers' interests and demands including their calendar, in-vestment capacity and economical horizon, progress concept, etc.
Biogas has been the main product from the digester publishedso far. However the use of biol (bio-slurry or effluent) has a highpotential to become the main result of the anaerobic digestion, dueto it close the agricultural production cycle treating the farmwaste,increasing the crop production, farmers income, reducing theexpansion of the agricultural frontier, reinforcing a non dependantagriculture from external chemical or ecological inputs, lookingforward to food sovereignty, and all this with an appropriateenergizing technology for mitigation and adaptation to climatechange.
Acknowledgments
Financial support to write this paper was provided by theEndev-Bolivia Program of the GIZ and Hivos, with the collaborationof the Research Center of Biodigesters, Biogas and Biol (CIB3,Bolivia) and the Caribbean and Latin American Biodigesters Net(RedBioLAC).
References
[1] World Energy Outlook (WEO). IEA. [cited March 2013]. Available from: http://www.iea.org/publications/freepublications/publication/English.pdf, ; 2012.
[2] IEA. Energy poverty: how to make modern energy access universal? [citedMarch 2013]. Available from: http://content.undp.org/go/cms-service/stream/asset/?asset_id¼2822269, ; 2010.
[3] Visser A, Khan HR. When smoke gets in your eyes: kitchen air quality in ruralBangladeshi homes. Energy Sustain Dev 1996;3(4):52e7.
[4] He K, Lei Y, Pan X, Zhang Y, Zhang Q, Chen D. Co-benefits from energy policiesin China. Energy; 2009. http://dx.doi.org/10.1016/j.energy.2008.07.021.
[5] Ward AJ, Hobbs PJ, Holliman PJ, Jones DL. Optimisation of the anaerobicdigestion of agricultural resources. Bioresour Technol 2008;99:7928e40.
[6] Yiridoe EK, Gordon R, Brown BB. Nonmarket co-benefits and economicfeasibility of on-Farm biogas. Energy Policy 2009;37:1170e9.
[7] Spagnoletta, Alessandro Sebastiano. Viability study for the application ofsmall-size bio-digesters in the Andean rural zone of Cajamarca (Peru) [MSc.Thesis]. European Master in Renewable Energy, Loughborough University;2007. On-site supervisors: E. Velo (GRECDH/UPC) and David Vilar (ISF).
[8] Martí-Herrero J. Transfer of low-cost plastic bio-digester technology at house-hold level in Bolivia. Livest Res Rural Dev 2007;19(12). Article #192. [citedMarch 2013]. Available from: http://www.lrrd.org/lrrd19/12/mart19192.htm.
[9] World development indicators and global development finance [cited March2013]. Available from: http://databank.worldbank.org/; 2012.
[10] Ghimire PC. SNV supported domestic biogas programmes in Asia and Africa.Renew Energy 2013;49:90e4.
[11] Bond T, Templeton MR. History and future of domestic biogas plants in thedeveloping world. Energy Sustain Dev 2011;15:347e54.
[12] Chen L, Zhao L, Ren C, Wang F. The progress and prospects of rural biogasproduction in China. Energy Policy 2012;51:58e63.
[13] Botero RB, Preston TR. Biodigestor de bajo costo para la producci�on de combus-tible y fertilizante a partir de excretas: manual para su instalaci�on, operaci�on yutilizaci�on.Cali, Colombia:CIPAV;1987.p. 20 [citedMarch2013].Available from:http://www.utafoundation.org/publications/botero%26preston.pdf.
[14] Xuan An Bui, Van Man Ngo, Nguyen Khang Duong, Duc Anh Nguyen,Preston TR. Installation and performance of low-cost polyethylene tube bio-digesters on small scale farms in Vietnam. In: Proc. National seminar-workshop sustainable livestock prod. on local feed resources. Ho Chi Minh:Agric. Pub House; 1994. pp. 95e103.
[15] Pound B, Bordas F, Preston TR. Characteristics of production and function of a 15cubic metre red-mud PVC biogas digester. Tropical Anim Prod 1981;6:146e53.
[16] Zhu Tracy. Assessment of small-scale biogas systems and their widespreaddissemination in can Tho City, Viet Nam. Independent Study Project (ISP)Collection; 2006. Paper 303.
[17] Lansing S, Botero R, Martin JF. Waste treatment and biogas quality in small-scale agricultural digesters. Bioresour Technol 2008a;99(13):5881e90.
[18] Ferrer I, Garfí M, Uggetti E, Ferrer-Martí L, Calderon A, Velo E. Biogas pro-duction in low-cost household digesters at the Peruvian Andes. BiomassBioenergy 2011;35:1166e674.
[19] Martí-Herrero J. Reduced hydraulic retention times in low-cost tubular di-gesters: two issues. Biomass Bioenergy 2011;35(10):4481e4.
[20] Martí-Herrero J, Cipriano J. Design methodology for low cost tubular digesters.Bioresour Technol 2012;108:21e7.
[21] Perrigault T, Weatherford V, Martí-Herrero J, Poggio D. Towards thermaldesign optimization of tubular digesters in cold climates: a heat transfermodel. Bioresour Technol 2012;124:259e68.
[22] Garfí M, Cadena E, P�erez I, Ferrer I. Technical, economic and environmentalassessment of household biogas digesters for rural communities. Renew En-ergy 2014;62:313e8.
[23] Martí-Herrero J, Acosta-Bedoya F, Gonzales L. Plan del programa nacional debiodigestores de Bolivia. Bolivia: La Paz; 2013. Hivos-SNV-SolucionesPr�actica-CIMNE. [cited January 2013]. Available from: http://www.snvworld.org/download/publications/snv-cimne-hivos_2013_-_plan_nacional_de_biodigestores_de_bolivia.pdf.
[24] Martí-Herrero J. Biodigestores Familiares. Guía de dise~no y manual deinstalaci�on. La Paz, Bolivia: Cooperaci�on T�ecnica Alemana-GTZ; 2008, ISBN978-99954-0-339-3 [cited March 2013]. Available from: http://books.google.es/books?id¼TsbrdcmKGKoC.
[25] Alvarez R, Villca S, Liden G. Biogas production from llama and cow manure athigh altitude. Biomass Bioenergy 2006;30:66e75.
[26] Lansing S, Viquez J, Martinez H, Botero R, Martin J. Quantifying electricitygeneration and waste transformations in a low-cost, plug-flow anaerobicdigestion system. Ecol Eng 2008b;34(4e5):332e48.
[27] Lansing S, Martin JF, Botero R, Nogueira da Silva T, Dias da Silva E. Methaneproduction in low-cost, unheated, plug-flow digesters treating swine manureand used cooking grease. Bioresour Technol 2010a;101(12):4362e70.
[28] Lansing S, Martin JF, Botero R, Nogueira da Silva T, Dias da Silva E. Wastewatertransformations and fertilizer value when co-digesting differing ratios ofswine manure and used cooking grease in low-cost digesters. Biomass Bio-energy 2010b;34(12):1711e20.
[29] Ferrer I, Gamiz M, Almeida M, Ruiz A. Pilot project of biogas production frompig manure and urine mixture at ambient temperature in Ventanilla (Lima,Peru). Waste Manag 2009;2009(29):168e73.
[30] Alvarez R, Liden G. Anaerobic co-digestion of aquatic flora and quinoa withmanures from Bolivian Altiplano. Waste Manag 2008a;28(10):1933e40.
[31] Alvarez R, Liden G. The effect of temperature variation on biomethanation athigh altitude. Bioresour Technol 2008b;99(15):7278e84.
[32] Alvarez R, Liden G. Low temperature anaerobic digestion of mixtures of llama,cow and sheep manure for improved methane production. Biomass Bioenergy2009;33:527e33.
[33] Garfí M, Gelman P, Comas J, Carrasco W, Ferrer I. Agricultural reuse of thedigestate from low-cost tubular digesters in rural Andean communities.Waste Manag 2011;31:2584e9.
[34] Garfí M, Ferrer-Martí L, Irene Perez I, Flotats X, Ferrer I. Codigestion of cowand guinea pig manure in low-cost tubular digesters at high altitude. Ecol Eng2011;37:2066e70.
J. Martí-Herrero et al. / Renewable Energy 71 (2014) 156e165 165
[35] Garfí M, Ferrer-Martí M, Velo E, Ferrer I. Evaluating benefits of low-costhousehold digesters for rural Andean communities. Waste Manag 2011;31:2584e9.
[36] Garfí M, Ferrer-Martí L, Villegas V, Ferrer I. Psychrophilic anaerobic digestionof guinea pig manure in low-cost tubular digesters at high altitude. BioresourTechnol 2011;102:6356e9.
[37] Mwirigi JW, Makenzi PM, Wo Ochola. 'Socio-economic constraints to adoptionand sustainability of biogas technology by farmers in Nakuru Districts, Kenya.Energy Sustain Dev 2009;13:106e15.
[38] Xuan An Bui. Biogas technology in developing countries: Vietnam case study.In: Proceedings bio-digester workshop. Thu Duc, Ho Chi Minh City, Vietnam:University of Agriculture and Forestry; 2002.
[39] Huang F, Zheng X, Gao Y. Actions and modes of household biogas for newrural area construction in China. Guangdong Agric Sci 2007;8:114e6.
[40] Nazir M. Biogas plants construction technology for rural areas. BioresourTechnol 1991;35:283e9.
[41] Kristoferson LA, Bokhalders V. Renewable energy technologies: their appli-cations in developing countries. London: Intermediate Technology Publica-tions; 1991. pp. 112e7.
[42] Walekhwa PN, Mugisha J, Drake L. Biogas energy from family-sized digestersin Uganda: critical factors and policy implications. Energy Policy 2009;37:2754e62.
[43] Arthur R, Baidoo MF, Antwi E. Biogas as a potential renewable energy source:a Ghanaian case study. Renew Energy 2011;36:1510e6.
