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?

rgupta@carollo.com