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Lifting the Fog from FOG Receiving
AZ Water Association
Biosolids Workshop 2020, Tucson, Arizona
Rashi Gupta, P.E. Carollo Engineers
February 4, 2020
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Acknowledgements
• Co-Authors:
− Daniel Meacham (Carollo, CA)
− Phil Parkins (Carollo, AZ)
− Travis A. Peacock (Albuquerque Bernalillo County Water Utility Authority, NM)
− Anthony L. Montoya (Albuquerque Bernalillo County Water Utility Authority, NM)
• Review:
− Gary Deis (Carollo, CA)
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Understanding the whole picture is necessary
for informed decision-making
• Water Authority knew that when it’s digested, FOG has many benefits
• Site visits and a detailed survey of existing facilities helped answer these questions
• Reduces clogs in collection system
• Decreases energy demand for treatment
• Produces energy… but, what issues do we have to consider?
… have facilities seen the expected benefits?
… and how do we make it successful?
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A real-life perspective from operational
systems provides a fuller picture
East Bay Municipal Utility District
City of Gresham
City of Los Angeles
Pinellas County
Johnson County
City of Riverside
City of Fresno
City of Thousand Oaks
Silicon Valley Clean Water
Sacramento Regional County Sanitation District
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Facility investigations were comprehensive
• Facility background and drivers
• FOG characteristics and quality control
• FOG receiving station equipment and cost
• FOG receiving station materials of construction
• O&M issues and requirements
• Impacts on digester gas production and revenue from tipping fees
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Facility Facts
• Plant Average Dry Weather Flow (ADWF) Capacity: 12.5 – 450 mgd
• FOG Receiving Station Capacity: 12,000 – 175,000 gpd
• FOG Receiving Station Storage Capacity: 5,000 –60,000 gallons
• Years of FOG Receiving Station Operation: 3 – 11 years
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Specific drivers initiated FOG projects
• Reduced utility costs through increased digester gas production
• Reduced clogging and impacts on collection system
• Improved sustainability and reduced greenhouse gas emissions
• Revenue generation
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FOG sources determine characteristics
• FOG is “brown grease” from restaurant grease traps
− Concrete, flatware, bones, etc.
• FOG typically delivered by private grease haulers (beware septage!)
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FOG characteristics illustrate variability
ParameterNumber of Facilities
Regularly Monitoring
Typical Frequency
of Measurementa
Range of Reported
Valuesb, (median)
Quantity of FOG
Received9
With delivery
or daily
1,500 – 105,000 gpd,
(18,500 gpd)
pH 5With delivery or
daily composite2 – 6 (4)
Total Solids (TS) 5With delivery or
daily composite0.5% - 20%, (8.6%)
Volatile Solids (VS) 5With delivery or
daily composite
Less than 20% to
100%, (79%)
Chemical Oxygen
Demand (COD)2
With delivery or
daily composite
5,000 – 202,000
mg/L, (50,000 mg/L)
a) Frequency of testing is based only on facilities that reported testing intervals and regularly monitored
parameters.
b) Some facilities indicated that they test for these parameters, but did not report measured values.
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FOG quality control is essential, but difficult
• Several facilities contract with single hauler
− Hauler provides consistent and prescreened material
• Seven of the surveyed facilities require haulers to apply for a permit
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The Generic Process
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Debris removal is the first line of defense
Bar Screen Basket Strainer
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Macerators/grinders chew up debris and rock
traps allow heavy materials to drop out
Inline Grinder Rock Trap/Macerator
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Offloading pumps control tanker discharge
Peristaltic Hose
Rotary Lobe
Centrifugal Chopper
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FOG tanks provide short term storage (and
“inadvertent” grit removal!)
Steel Horizontal
Vertical FRP
Vertical Steel – Cone Bottom
Vertical Stainless Steel
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Recirculation pumps can provide multiple
functions
Centrifugal Chopper Rotary Lobe
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Heating systems keep material flowing and
reduce clogs/mats
• Heat Exchangers
• Heat Tracing
• Insulation
• Preheated FOG
• Steam Injection
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Digester feed pumps meter FOG into
digesters, typically with VFDs
Progressing Cavity Rotary Lobe
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Odor control requirements driven by area and
neighbors
Bioreactor Carbon Canister Scrubber
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Materials tell a “tale of two cities”
Stainless Steel Glass-Lined Ductile Iron
NBR (Buna-N) Hose PVC
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Isolation valves critical for O&M but subject
to extremely severe duty
Ductile Iron Plug
Valves with Buna-N
Full Port PVC
Ball Valves
Full Port SST
Ball Valves
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Reported construction costs follow size, but
also redundancy, complexity, automation
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
$0.0
$0.5
$1.0
$1.5
$2.0
$2.5
$3.0
$3.5
$4.0
A
(2015)
B
(2010)
C
(2013)
D
(2011)
E
(2008)
F
(2013)
G
(2011)
FO
G T
an
k C
ap
acit
y, g
al
Co
nst
ructi
on
Co
st, $
Mil
lio
n
Facility (Year Constructed)
Storage Tank Capacity Construction Cost
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System changes frequent post-startup
• Reasons for equipment changes:
− Increase service life
− Reduce maintenance needs
− Combat abrasive and corrosive nature of FOG
• Add screening/straining
• Add heating
• Replace steel components with stainless steel
• Try various elastomers for pumps and valves
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O&M issues are real and significant
• Facilities agreed that FOG is a difficult material to handle
Abrasive Acidic Variable Odorous Labor intensive
• In most cases, labor required was higher than anticipated
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FOG delivery control can reduce staff time OR
improve quality/consistency
• Key card system
− Allows delivery during non-staffed hours
− Restricts delivery to permitted haulers
− Difficult to implement sample testing
− No operator assistance/control
• Operator presence required
− Operator controls/oversees offloading
− Operators can sample each delivery
− More staff time required
− Haulers are time-limited for delivery
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O&M Issues: Screens, Strainers, and Macerators
Clogging Corrosion Abrasion
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O&M Issues: Pumps
• Damage/wear of elastomers (replacement: 3 – 6 months)
• Damage/wear of pump housings (replacement: 6 – 36 months)
• Damage/wear to internal components(replacement: as needed)
Maintenance and replacement more
frequent than same pumps for sludge
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O&M Issues: Valves, Piping, and Storage
Grit, Debris, and
Rocks
Grease Clogging and
Mat Formation
Damage to Elastomers
in Valves
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Staff time required for more than just O&M
• In addition to O&M of FOG system, staff required for:
− Permitting haulers and monitoring for compliance
− Inspecting FOG loads, sample collection and analysis
− Monitoring digester performance and troubleshooting
− Determination and collection of tipping fees
− Management of contracts, if any, with FOG haulers
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Reported staffing requirements must be
considered in economics
1 1
1 - 2 2
0.25
0
0.5
1
1.5
2
2.5
A B C D E
No
. Fu
ll T
ime E
mp
loyees
Facility
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Digester stability paramount, but no standard
feed control (yet)
• Multiple methods used:
− Empty FOG tank over setpoint time
− FOG tank level control
− FOG slowly fed in increasing amounts for acclimation
− Maintain total or volatile solids loading to digester
− Specific FOG:sludge feed ratio by volume
− Specific volume per day
− Vary to optimize gas production
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Changes in gas production are significant
FOG digestion played a key role in energy neutrality for two facilities
100%
30%
57%
57 – 97% 100%
0
20
40
60
80
100
120
A B C D E
Perc
en
t In
cre
ase
in
Gas
Pro
du
cti
on
Facility
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Variation in delivery impacts gas production
– mitigate through FOG and/or gas storage
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
19-Aug 29-Aug 8-Sep 18-Sep 28-Sep 8-Oct 18-Oct
FOG Delivered, gal
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Tipping fees and revenue often drive system
economics – but are not guaranteed
• Two agencies reported $300,000/year of revenue from tipping fees
• Highly dependent on local market, which may change over time
$0.08
$0.09
$0.03
$0.01
$0.08
$0.00
$0.02
$0.04
$0.06
$0.08
$0.10
A B C D E
$/g
all
on
Facility
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The evolution of HSW receiving offers some
solutions to screening and contaminant
removal
• Flo-Beast at SVCW
• Modified system for FOG applications
− U-shaped inlet flush header
− Auxiliary hot water connection
− Booster pumps
• 7 US Installations on FOG or food waste
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The evolution of HSW receiving offers some
solutions to screening and contaminant
removal
• Strainpress at Napa
• 22 HSW installations in Europe on up to 15% solids
• May require heating and dilution
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Proper planning, stakeholder buy-in, and
design based on lessons-learned critical to
success
• FOG receiving offers multiple benefits, including a path towards energy independence
• Before embarking, consider:
• Drivers and operational goals
• Quantity and quality of material available
• FOG market in area/realistic tipping fees
• Economics specific to each case
• Other goals may supersede economics for some facilities
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Proper planning, stakeholder buy-in, and
design based on lessons-learned critical to
success
• FOG receiving is O&M intensive
• Successful, sustainable operations possible through:
− System design based on lessons-learned
− Strong, preventative O&M program
− Early consensus from all stakeholders
• Two plants have achieved energy neutrality/net positive status, partly due to FOG receiving and digestion
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We would like to thank all facilities that
participated in the survey and shared
their experiences.
AND THANK YOU FOR LISTENING!
Questions?