OPERATIONAL CONSIDERATIONS FOR CO-DIGESTION

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1 OPERATIONAL CONSIDERATIONS FOR CO-DIGESTION California Water Environment Association SARBS Seminar on Math, Operations and Maintenance for Biosolids Systems September 2011 Fred Soroushian, P.E. PE CH2M HILL

Seminar on Math, Operations and Maintenance for

2 PRESENTATION OVERVIEW Co-digestion overview Co-digestion i feedstock Bench scale testing Co-digestion implementation and business model

3 CO-DIGESTION OVERVIEW

4 CODIGESTION OVERVIEW BENEFITS OF CO-DIGESTION Solves environmental problem and increases renewable energy production Increase in gas and energy production Reduced load and energy demand for wastewater treatment Optimized gas production during peak power demand Efficient use of existing infrastructure More efficient compared to pretreatment at each sources Potential reduction in sewer system odors, blockage, and GHG emissions

Optimized gas production during peak power demand Efficient use of existing infrastructure More efficient

5 CO-DIGESTION OVERVIEW - DRAWBACKS OF CO-DIGESTION Increases WWTP direct loads Changes C/N ration in influent when high h C, low N substrate t is directed d to digesters Need additional facilities for codigestion Substrate must be trucked-in May need additional pretreatment

substrate t is directed d to digesters Need additional facilities

6 CO-DIGESTION POTENTIAL IN CA Scenario Biogas (million cf/d) without with Co- Codigestiodigestion Electricity (MW) without with Co- Codigestiodigestion Scenario (all 312 STPs) Scenario (114 STPs with ADs) Biosolids : Food Waste = 80 : 20 by volume for codigestion Biogas can be increased by 58% with co-digestion 60 MW increase

155 223 352 (all 312 STPs) Scenario 2 45 71 102 161 (114 STPs with ADs) Biosolids : Food

7 CO-DIGESTION EXPERIENCE North America East Bay MUD, Riverside, IEUA, Watsonville, Millbrae, and CMSA, CA West Lafayette, IN Pendleton, OR Lethbridge and Edmonton, Canada Europe Denmark >100 Germany >10 Italy, Hungary, Poland, etc.

Lafayette, IN Pendleton, OR Lethbridge and Edmonton,

8 CO-DIGESTION FEEDSTOCK Many feedstock sources: FOG Breweries and distilleries Dairy Food manufacturers Baking industry Slaughter houses FOG, meat, fish, dairy, and fruit wastes produce most gas Issues include preservatives, other additives, and contaminants

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

9 CO-DIGESTION FEEDSTOCK Science of co-digestion is not well known Limited available data Current knowledge is site-specific ifi and often not transferable to other facilities Bench scale testing allows different food wastes to be evaluated for co-digestion Co-digestion g operation Blend ratios Dewaterability Dewatering filtrate quality

facilities Bench scale testing allows different food wastes to be evaluated for

10 BENCH SCALE TEST SETUP

11 BENCH SCALE TEST SETUP Source: Jörg Krampe, SA Water Corporation, 2011

12 BENCH SCALE TEST PLAN Simulate anaerobic digester conditions Use digester sludge as inoculums 20 days retention time Mesophilic or thermophilic conditions to match digester operations Test various concentrations ti of substrate t mixtures 0% Reference 5% 10% 15% 20% 30% 50% Expected operation level Inhibition/Overloading

match digester operations Test various concentrations ti of substrate t mixtures

13 BENCH SCALE TEST GAS PRODUCTION Source: Jörg Krampe, SA Water Corporation, 2011

14 BENCH SCALE TEST GAS PRODUCTION Mesophilic Digestability Tests Gas Produc ction (ml) Control Tomato Salad Dressing Cheese 50:50 blend digestibility testing Mesophilic Thermophilic Thermophilic Digestability Tests Day of Test Gas Production (m ml) Control Tomato Salad Dressing Cheese Day of Test

11 13 15 17 19 21 23 25 27 Thermophilic Digestability Tests Day of Test 4000 3500 Gas Production (m ml) 3000

15 CO-DIGESTION IMPLEMENTATION Food waste sources identification Bench scale digestion testing Digester Loading Typically limit to 20 to 30% of digester VS feed Continuous feed if possible Optimum C:N ratio of Receiving station Screens blending/mixing Heating

20 to 30% of digester VS feed Continuous feed if possible Optimum

16 CO-DIGESTION IMPLEMENTATION Digestion system process modifications/ improvements Food waste flow distribution and measurement Gas collection, treatment and co-generation infrastructure improvements Solids handling systems assessment Dewatering e system operation o Recycle management

collection, treatment and co-generation infrastructure improvements

17 POTENTIAL BUSINESS MODEL

18 CO-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 Salty Whey Chicken blood Brewery Cola based alcoholic beverage waste Source: Jörg Krampe, SA Water Corporation, 2011

36 4.22 Salty Whey 4.36 7.82 3.47 Chicken blood 37.00 14.37-22.63 Brewery 1.08 3.63 2.

19 CO-DIGESTION IMPLEMENTATION Food Waste Receiving, Storage and Feed System

20 CO-DIGESTION IMPLEMENTATION Food Waste Receiving, Storage and Feed System

21 CO-DIGESTION PERFORMANCE RP-1 Digester 4 Volatile Solids Reduction 15-day Running Average % VSR 80% 70% 60% 50% 40% 30% 20% 10% Baseline Operation Manure Foodwaste Codigestion 11% Points Improvement 0% 11/29/2004 1/18/2005 3/9/2005 4/28/2005 6/17/2005 8/6/2005 9/25/ /14/2005 1/3/2006

22 CO-DIGESTION PERFORMANCE Observed Acclimized System Average Biogas RP-1 Digester 4 Biogas Production Expected Biogas kcfd Baseline Codigestion

23 CO-DIGESTION IMPLEMENTATION Slug feeding of digesters not recommended d 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

24 QUESTIONS? Thanks! WEFTECH 2005

St. Petersburg, FL: Vehicle Use of Recycled Natural Gas Derived from Wastewater Biosolids

U.S Department of Energy - Biomass 2014 St. Petersburg, FL: Vehicle Use of Recycled Natural Gas Derived from Wastewater Biosolids William Eleazer, PE Project Design Manager John Willis, PE, BCEE Project