This document summarizes a presentation on receiving and handling fats, oils, and grease (FOG) at wastewater treatment facilities. It discusses results from a survey of 10 facilities on their FOG receiving processes, equipment used, operation and maintenance issues, impacts on digester gas production, and economics. Key findings included highly variable FOG characteristics, significant increases in digester gas production from FOG digestion, and higher than expected operation and maintenance costs due to the abrasive nature of FOG. Facilities reported changing equipment to increase durability and adopting different feeding methods to optimize digester performance over time. Economics depended strongly on local tipping fee rates and quantity of FOG received. The presentation concluded that successful F

1. Lifting the Fog from FOG Receiving
WEFTEC New Orleans, Louisiana
Rashi Gupta, P.E.
Carollo Engineers
September 27, 2016

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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, materials, and cost
• 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
Parameter
Number of Facilities
Regularly Monitoring
Typical Frequency
of Measurementa
Range of Reported
Valuesb, (median)
Quantity of FOG
Received
9
With delivery
or daily
1,500 – 105,000 gpd,
(18,500 gpd)
pH 5
With delivery or
daily composite
2 – 6 (4)
Total Solids (TS) 5
With delivery or
daily composite
0.5% - 20%, (8.6%)
Volatile Solids (VS) 5
With 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
$4.0
A
(2015)
B
(2010)
C
(2013)
D
(2011)
E
(2008)
F
(2013)
G
(2011)
FOGTankCapacity,gal
ConstructionCost,$Million
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.FullTimeEmployees
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
PercentIncreaseinGas
Production
Facility

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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
$/gallon
Facility

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The Big Picture
• 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
• No silver bullet for materials/equipment, but design based
on lessons learned and a strong O&M program can make
FOG receiving successful.
• Gain consensus from all stakeholders.
− FOG receiving is O&M intensive, but offers multiple benefits,
including a path towards energy independence.

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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?