Food Waste Digestion in Water and Sludge Daniel Gary, Rob Morton and Chi-Chung Tang
Los Angeles County Sanitation Districts LANCASTER Solid waste disposal; wastewater collection and treatment for half of Los Angeles County population SANTA CLARITA Pacific Ocean LA CANADA FLINTRIDGE PALMDALE GLENDALE SIE RRA MA DRE PASADENA MONROVIA DUA RTE AZUSA GLENDORA ARCADIA SAN MARINO CLA REMONT IRWINDALE SAN DIMAS SAN GABRIEL WEST HOLLYWOOD ALHAMBRA COVINA LA VERNE BEVERLY HILLS EL MONTE WEST COVINA ROSEMEAD POM ONA MONTEREY PARK LA PUE NTE WALNUT MONTEBELLO CITY OF INDUSTRY VERNON PICO RIVERA DIAMOND BAR BELL WHITTIER INGLEWOOD LA HAB RA HE IGHTS SOUTH GATE SANTA FE SPRINGS DOWNEY EL SEGUNDO LYNW OOD HAWTHORNE PARAMOUNT NORW ALK GARDE NA COMPTON BELLFLOWER LA MIRADA MANHATTA N BEACH CERRITOS REDONDO BEACH LAKEW OOD CARSON TORRANCE HAWAIIAN GARDENS SIGNAL HILL LOMITA LONG BEACH PALOS VERDES ESTATES ROLLING HILLS RANCHO PALOS VERDES LOS ANGELES
Need to Address Alternatives to Landfilling Food Wastes 16% of wastes in landfills are food wastes (CalRecycle) Limited remaining landfill spaces locally Method to reduce green house gas emissions Can convert some food wastes to energy and reduce the volume of food waste requiring disposal
Project Goals Determine if it is feasible to digest 10-30% by weight food wastes in waste water sludge and in water Characterize food wastes Provide some economic data for determining full-scale operation costs
Brief Review of Digestion Stabilize sludge and reduce vector attraction Bacteria convert organics (such as wastewater sludge, food waste) into cellmass and vapor, reducing the total amount of solids in the digested product
Brief Review of Digestion Different operating temperatures (this study mesophilic 95 o F) and with or without air (this study anaerobic) Energy recovery can occur if anaerobically digested - methane is produced
Anaerobic Digestion Process Starting Products Liquefaction Acid Production Biogas Production End Products Hydrolytic Bacteria Acid Forming Bacteria Methane Forming Bacteria Sludge from JWPCP or Water Liquefied soluble organic compounds Simple organic acids Digester gas Food Wastes Insoluble compounds (inorganic, organic, water) Biosolids
Other California Food Waste Digestion Projects EBMUD co-digestion of food wastes with sludge at Oakland facility U.C. Davis On-Site Power digesting food wastes for commercial application in food packaging facilities Novato digesting food wastes City of Los Angeles pilot program digesting food wastes
East Bay Municipal Utility District Food Waste Preparation
EBMUD Paddle Finisher Paddle finisher results in a slurry, which aids in hydrolysis step of digestion
JWPCP Research Project Commencement Obtain food waste Set up and start bench scale digesters with sludge as media and with water as media Set up program to pre-treat food wastes, removing non-organics and reduce particle size (aid in hydrolysis)
JWPCP Operation 4 M gallon each 18 day solids retention time (SRT) 75% primary solids/ 25% TWAS JWPCP Research Study Bench Scale 10 Liter 18 day SRT 75% primary solids/ 25% TWAS Bench Scale digesters perform similarly to full scale digester
Food Waste Sources Vendor No. 1 Private waste handler Classifies residential wastes Vendor No. 2 LACSD material separation & transfer station Food waste from malls
JWPCP Research Food Waste Conditioning Program Screened, 0.25-0.5 kitchen scraps with extraneous matter Meat Grinder Grinded product 0.125-0.25 pellets Pure food wastes 3-10% hand-picked rejects (mostly metal, plastics, glass) Blended Digester Feed Water or sludge
Vendor No. 1 20% Food Waste Volatile Solids Destruction 100% 80% Control Food Wastes/H2O Food Waste/Sludge Avg Control Dig. = 50.4% Avg Food Waste/H20 = 59.3% Avg Food Waste/Sludge = 56.3% 60% VSD 40% 20% FW Batch 1 FW Batch 2 0% 08/02/08 08/17/08 09/01/08 09/16/08 10/01/08 10/16/08 10/31/08
Vendor No. 1 20% Food Waste Volatile Solids Destruction 100% 80% Control Food Wastes/H2O Food Waste/Sludge Avg. Control Dig. = 56.0% Avg. Food Waste/H20 = 36.8%; Avg. Food Waste/Sludge 43.5% 60% VSD 40% 20% 0% Food Wastes Batch 3 Food Wastes Batch 4 12/28/08 1/12/09 1/27/09 2/11/09 2/26/09 3/13/09 3/28/09
Vendor No. 1 20% Food Waste Gas Production 25 20 Control Food Wastes/H2O Food Waste/Sludge Avg. Control Sludge = 6.19 Avg. Food Waste/H2O = 13.4 Avg. Food Waste/Sludge = 16.4 Gas Prod. L/Day 15 10 5 0 FW Batch 1 FW Batch 2 8/10/08 8/30/08 9/19/08 10/9/08 10/29/08
20 16 Vendor No. 1 20% Food Waste Gas Production Control Food Wastes/H2O Food Waste/Sludge Avg. Control Sludge = 7.75 Avg. Food Waste/H2O = 5.85 Avg. Food Waste/Sludge = 10.2 Gas Prod. L/Day 12 8 4 0 Food Wastes Batch 3 Food Wastes Batch 4 12/30/08 1/14/09 1/29/09 2/13/09 2/28/09 3/15/09
Vendor No. 1 BOD of 20% Food Wastes For Different Batches (varies from batch to batch) 50,000 44,400 40,000 BOD mg/l 30,000 20,000 19,100 27,700 22,200 24,600 15,800 17,800 10,000 11,100 0 Control Sludge First Batch Second Batch Third Batch Fourth Batch
Why Different Vendor No. 1 Batches had Different BODs and Digestion Performances Food Waste from Vendor 1 was small kitchen wastes Black and dirt like, not specifically food wastes Different batches had varying amounts of yard clippings and dirt
Vendor No. 2 Food Wastes
Vendor No. 2 BOD of Different Batches 50,000 (Waste Source More Consistent) BOD mg/l 40,000 30,000 20,000 19,100 28,000 33,000 31,000 39,000 10,000 0 Control Sludge 1 2 3 4 Batch
100% Volatile Solids Destruction Vendor No. 2 10% Food Waste vs. Control Sludge 80% 60% 40% 20% Control Sludge Food Wastes/H2O Food Wastes/Sludge Avg. Control Sludge = 53.8% Avg. Food Wastes/H2O = 93.8% Avg. Food Wastes/Sludge =81.8% 0% 06/14/09 06/24/09 07/04/09 07/14/09 07/24/09 08/03/09 08/13/09
35 30 Gas Production Vendor No. 2 10% Food Waste vs. Control Sludge Control Sludge Food Waste/H2O Food Waste/Sludge Avg. Control Sludge =6.93 L/day Avg. Food Waste/H2O = 12.0 L/day Avg. Food Waste/Sludge = 20.6 L/day 25 Gas Prod. L/Day 20 15 10 5 0 06/13/09 06/23/09 07/03/09 07/13/09 07/23/09 08/02/09 08/12/09
100% Volatile Solids Destruction Vendor No. 2 20% Food Waste vs. Control Sludge 80% VSD 60% 40% 20% Control Sludge Food Waste/H2O Food Waste/Sludge Avg. Control Sludge = 54.9% Avg. Food Waste /H2O = 76.6% Avg. Food Waste/Sludge = 75.2% 0% 08/11/09 08/21/09 08/31/09 09/10/09 09/20/09 09/30/09 10/10/09 10/20/09
Gas Production Vendor No. 2 20% Food Waste vs. Control Sludge 40 35 30 Control Sludge Food Waste/H2O Food Waste/Sludge Avg. Control Sludge =6.86 L/day Avg. Food Waste/H2O = 6.79 L/day Avg. Food Waste/Sludge = 24.9 L/day Gas Prod. L/Day 25 20 15 10 5 0 08/11/09 08/21/09 08/31/09 09/10/09 09/20/09 09/30/09 10/10/09 10/20/09
Volatile Solids Destruction Vendor No. 2 30% Food Waste vs. Control Sludge 100% 80% Control Sludge Food Waste/Sludge Avg. Control Sludge = 52.8% Avg. Food Waste/Sludge = 65.3% VSD 60% 40% 20% 0% 10/18/09 11/02/09 11/17/09 12/02/09 12/17/09
Gas Production Vendor No. 2 30% Food Waste vs. Control Sludge 30 25 Control Sludge Food Waste/Sludge Avg. Control Sludge = 6.38 L/Day Avg. Food Waste/ Sludge. = 19.5 L/Day Gas Prod. L/Day 20 15 10 5 0 10/15/09 10/25/09 11/04/09 11/14/09 11/24/09 12/04/09 12/14/09
Summary Vendor No. 2 Volatile Solids Destruction 100% 80% 10% 20% 30% 93.8% 76.6% 81.8% 75.2% 60% 54.9% 53.8% 52.8% 65.3% VSD 40% 20% 0% Control Water Sludge
Summary Vendor No. 2 Digester Gas Production 30 25 20 10% 20% 30% 20.6 24.9 19.5 Gas Prod. 15 L/Day 12.0 10 6.9 6.9 6.4 6.8 5 0 Control Water Sludge
Volatile Acids 10,000 1,000 10% 20% 30% 5,380 350 400 Volatile Acids mg/l 100 10 11 21 30 46 16 1 Control Water Sludge
Optimal Weight % Food Waste 10% food waste in sludge Chance of building up volatile acids if digested in water Minimum amount of non-digested solids build up in digesters at 10% food waste digestion in sludge
Initial Economic Feasibility Analysis Digest using 10% food waste/90% sludge Size for 100 tons/week food wastes - EBMUD size - (Modifications estimated to cost $1M) Use methane gas to offset imported natural gas Can charge a tipping fee for food waste of $10/ton Costs for extra solids discharged from wastewater treatment plant, O & M, and capital costs
100 Tons/Week Food Waste Initial Economic Feasibility Analysis Savings/Income or Cost Annual savings and receipts Charge Tipping Fee Tipping fee $ 50,000 $0 No Tipping Fee Not importing natural gas $250,000 $250,000 Total annual savings $300,000 $250,000 Annual costs Amortized capital $ 60,000 $ 60,000 Non-digested food wastes disposal $140,000 $140,000 Operation and maintenance $ 50,000 $ 50,000 Total annual cost $250,000 $250,000 Total annual benefit $ 50,000 $0
Conclusion Source of food waste is important Readily soluble, High BOD Determined 10% food waste digestion in sludge was optimal method Produce more digester gas but get more nondigested solids in effluent from the digester Modifications to energy recovery hardware and contract need to occur to make food waste digestion economical at the JWPCP
Questions
Future Work Dewatering Test -- to what percentage can food wastes/sludge composite be dewatered Economic comparison digestion vs. composting food waste Conduct a large scale test at Joint Water Pollution Control Plant Conduct a large scale test at another LACSD Facility (landfill or wastewater treatment plant)
Potential Food Waste Digestion Applications for LACSD Closing local landfill in 2013 and will transport solid waste to remote landfill in Imperial County (over 1M lbs food waste/day) No energy recovery available yet at remote landfill Potential to digest at various treatment plants