OPERATIONAL CONSIDERATIONS FOR CO DIGESTION OPERATIONAL CONSIDERATIONS FOR CO DIGESTION CO-DIGESTION

California Water Environment Association

CO-DIGESTION

California Water Environment AssociationCalifornia Water Environment AssociationSARBS Seminar on Math, Operations and Maintenance for Biosolids Systems

California Water Environment AssociationSARBS Seminar on Math, Operations and Maintenance for Biosolids SystemsMaintenance for Biosolids SystemsSeptember 2011Maintenance for Biosolids SystemsSeptember 2011

F d S hi P EF d S hi P EFred Soroushian, P.E.CH2M HILL Fred Soroushian, P.E.CH2M HILL

PRESENTATION OVERVIEWPRESENTATION OVERVIEWPRESENTATION OVERVIEWPRESENTATION OVERVIEW

Co-digestion overview

C di i f d kCo-digestion feedstock

Bench scale testing

Co-digestion implementation and business model

CWEA 2011

CO DIGESTION OVERVIEWCO DIGESTION OVERVIEWCO-DIGESTION OVERVIEWCO-DIGESTION OVERVIEW

CWEA 2011

CODIGESTION OVERVIEW – BENEFITS CODIGESTION OVERVIEW – BENEFITS CODIGESTION OVERVIEW BENEFITS OF CO-DIGESTIONCODIGESTION OVERVIEW BENEFITS OF CO-DIGESTION

S l i l bl d i bl Solves environmental problem and increases renewable energy production

Increase in gas and energy production Increase in gas and energy production

Reduced load and energy demand for wastewater treatmenttreatment

Optimized gas production during peak power demand

Efficient use of existing infrastructure Efficient use of existing infrastructure

More efficient compared to pretreatment at each sources

Potential reduction in sewer system odors blockage and Potential reduction in sewer system odors, blockage, and GHG emissions

CWEA 2011

CO-DIGESTION OVERVIEW - DRAWBACKS CO-DIGESTION OVERVIEW - DRAWBACKS OF CO-DIGESTIONOF CO-DIGESTION

Increases WWTP direct loads

Changes C/N ration in influent when hi h C l N b t t i di t d thigh C, low N substrate is directed to digesters

Need additional facilities for co- Need additional facilities for co-digestion

Substrate must be trucked-in

May need additional pretreatment

CWEA 2011

CO-DIGESTION POTENTIAL IN CACO-DIGESTION POTENTIAL IN CACO DIGESTION POTENTIAL IN CACO DIGESTION POTENTIAL IN CA

Scenario

Biogas(million cf/d)

Electricity (MW)

without C

with C

without C

with CCo-

digestionCo-

digestionCo-

digestionCo-

digestion

Scenario 1 98 155 223 352(all 312 STPs)

Scenario 2 45 71 102 161(114 STPs with ADs)

Biosolids : Food Waste = 80 : 20 by volume for coBiosolids : Food Waste = 80 : 20 by volume for co-digestion Biogas can be increased by 58% with co-digestion 60 MW increase

CWEA 2011

CO DIGESTION EXPERIENCECO DIGESTION EXPERIENCECO-DIGESTION EXPERIENCECO-DIGESTION EXPERIENCE

North America East Bay MUD, Riverside, IEUA, Watsonville, East Bay MUD, Riverside, IEUA, Watsonville,

Millbrae, and CMSA, CA

West Lafayette, IN

Pendleton OR Pendleton, OR

Lethbridge and Edmonton, Canada

Europep Denmark >100

Germany >10

Italy, Hungary, Poland, etc.

CWEA 2011

CO DIGESTION FEEDSTOCKCO DIGESTION FEEDSTOCKCO-DIGESTION FEEDSTOCKCO-DIGESTION FEEDSTOCK

Many feedstock sources: Many feedstock sources: • FOG• Breweries and distilleries• Dairy• Food manufacturers

B ki i d• Baking industry• Slaughter houses

FOG meat fish dairy and fruit wastes produce FOG, meat, fish, dairy, and fruit wastes produce most gas

Issues include preservatives, other additives, and contaminants

CWEA 2011

CO DIGESTION FEEDSTOCKCO DIGESTION FEEDSTOCKCO-DIGESTION FEEDSTOCKCO-DIGESTION FEEDSTOCK

S i f di ti i t ll k Science of co-digestion is not well known

Limited available data

C k l d i i ifi d f Current knowledge is site-specific and often not transferable to other facilities

Bench scale testing allows different food wastes to be Bench scale testing allows different food wastes to be evaluated for co-digestionCo-digestion operationg pBlend ratiosDewaterabilityDewatering filtrate qualityDewatering filtrate quality

CWEA 2011

BENCH SCALE TEST SETUPBENCH SCALE TEST SETUPBENCH SCALE TEST SETUPBENCH SCALE TEST SETUP

CWEA 2011

BENCH SCALE TEST SETUPBENCH SCALE TEST SETUPBENCH SCALE TEST SETUPBENCH SCALE TEST SETUP

Source: Jörg Krampe, SA Water Corporation, 2011CWEA 2011

BENCH SCALE TEST PLANBENCH SCALE TEST PLANBENCH SCALE TEST PLANBENCH SCALE TEST PLAN

Si l t bi di t diti Simulate anaerobic digester conditions• Use digester sludge as inoculums• 20 days retention time20 days retention time• Mesophilic or thermophilic conditions to match digester

operations

T t i t ti f b t t i t Test various concentrations of substrate mixtures• 0% Reference• 5%

10%• 10%• 15%• 20%• 30%

Expected operation level

30%

• 50%Inhibition/Overloading

CWEA 2011

BENCH SCALE TEST GAS PRODUCTIONBENCH SCALE TEST GAS PRODUCTIONBENCH SCALE TEST GAS PRODUCTIONBENCH SCALE TEST GAS PRODUCTION

Source: Jörg Krampe, SA Water Corporation, 2011

BENCH SCALE TEST GAS PRODUCTIONBENCH SCALE TEST GAS PRODUCTION

Mesophilic Digestability Tests

BENCH SCALE TEST GAS PRODUCTIONBENCH SCALE TEST GAS PRODUCTION

50:50 blend digestibility testing Mesophilic2000

2500

3000

ctio

n (m

L)

ControlTomato

Thermophilic

0

500

1000

1500

Gas

Pro

duc Tomato

Salad DressingCheese

01 3 5 7 9 11 13 15 17 19 21 23 25 27

Day of Test

Thermophilic Digestability Tests

3000

3500

4000

mL)

1000

1500

2000

2500

3000

Gas

Pro

duct

ion

(m

ControlTomato Salad DressingCheese

0

500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Day of Test

G

CO DIGESTION IMPLEMENTATIONCO DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATION

Food waste sources identification Bench scale digestion testing Digester Loading

• Typically limit to 20 to 30% of digester VS feedC ti f d if ibl• Continuous feed if possible

• Optimum C:N ratio of 20-30 Receiving station Receiving station

• Screens• blending/Mixing• Heating

CWEA 2011

CO DIGESTION IMPLEMENTATIONCO DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATION

Digestion system process modifications/ improvements

f• Food waste flow distribution and measurement• Gas collection, treatment and co-generation infrastructure

improvementsimprovements

Solids handling systems assessment• Dewatering system operatione a e g sys e ope a o• Recycle management

CWEA 2011

POTENTIAL BUSINESS MODELPOTENTIAL BUSINESS MODELPOTENTIAL BUSINESS MODELPOTENTIAL BUSINESS MODEL

CO DIGESTION COST BENEFIT ANALYSISCO DIGESTION COST BENEFIT ANALYSISCO-DIGESTION COST - BENEFIT ANALYSISCO-DIGESTION COST - BENEFIT ANALYSIS

Substrate Total cost of addition of 1 kL

substrate ($)

Total benefit of addition of 1 kL

substrate ($)

Total profit per kL added ($)

Sweet Whey 2.14 6.36 4.22Salty Whey 4.36 7.82 3.47y yChicken blood 37.00 14.37 -22.63Brewery 1.08 3.63 2.55Cola based 0 26 27 23 26 97Cola based alcoholic beverage waste

0.26 27.23 26.97

Source: Jörg Krampe SA Water Corporation 2011Source: Jörg Krampe, SA Water Corporation, 2011

CWEA 2011

CO DIGESTION IMPLEMENTATIONCO DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATION

Food Waste Receiving, Storage and Feed System

CWEA 2011

CO DIGESTION IMPLEMENTATIONCO DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATION

Food Waste Receiving, Storage and Feed System

CWEA 2011

System

CO DIGESTION PERFORMANCECO DIGESTION PERFORMANCECO-DIGESTION PERFORMANCECO-DIGESTION PERFORMANCE

RP-1 Digester 4 Volatile Solids Reduction 15-day Running Average

70%

80%Baseline Operation Manure Foodwaste Codigestion

40%

50%

60%

VS

R

11% Points

10%

20%

30%% 11% Points Improvement

0%11/29/2004 1/18/2005 3/9/2005 4/28/2005 6/17/2005 8/6/2005 9/25/2005 11/14/2005 1/3/2006

CO DIGESTION PERFORMANCECO DIGESTION PERFORMANCECO-DIGESTION PERFORMANCECO-DIGESTION PERFORMANCE

RP-1 Digester 4 Biogas Production

270

180

210

240

Expected Biogas

Observed Acclimized System Average Biogas

120

150

180

kcfd

30

60

90

0

30

Baseline Codigestion

CO-DIGESTION IMPLEMENTATIONCO-DIGESTION IMPLEMENTATION

Sl f di f di t t d d

CO DIGESTION IMPLEMENTATIONCO DIGESTION IMPLEMENTATION

Slug feeding of digesters not recommended

Monitor delivered waste pH and %TS

Mesophilic conditions appears to be less sensitive to feed fluctuations; high activity in thermophilic can result in sour conditions more rapidly

Need to consider SRT in digester – maximize digestion time while allowing capacity for food waste

Sludge dewaterability, gas quality and filtrate quality need to be monitored at full-scale

CWEA 2011

QUESTIONSQUESTIONS ?QUESTIONSQUESTIONS ?

Thanks !

WEFTECH 2005CWEA 2011