Biogas Production from Municipal Organic Solid Wastes

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Abigail Fisher
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1 Biogas Production from Municipal Organic Solid Wastes Ruihong Zhang 1, Petros Gekas 1, Baoning Zhu 1,James Lord 2, Chris Choate 2 1 University of California, Davis 2 Norcal Waste Systems, Inc.

2 Municipal Solid Waste (MSW) Generation and Management in United States Amount 250 million tons per year 32% recycled 68% landfilled Composition 65% Biodegradable (paper, yard trimmings, food scraps, wood) 35% Non biodegradable (plastic, metals, rubber, glass, etc.) US EPA

3 Separation of Biodegradable Materials from MSW Source separation before collection Separation after collection Mechanical separation by density and size Thermal or biological treatment combined with mechanical separation Thermal treatment heating and steam explosion Biological treatment rotating drum reactor (RDR) (commercial names: Bedminster, Biomixer)

5 Organics Raw MSW Inorganics

6 Operating Conditions of RDR Process Batch or continuous with daily feeding Desirable Moisture Content of Feed: 50 60% Temperature in Drum: C Retention Time: 6 hours to 5 days Aeration Using Air Blowers

7 MSW TREATMENT PLANTS USING RDR LOCATION OPENED NO. OF DRUMS PLANT CAPACITY t/d Big Sandy, TX Pinetop-Lakeside, AZ Sevierville, TN Sorel-Tracy, QC, Canada Cobb Country, GA Rapid City, SD Sumter County, FL Marlborough, MA Nantucket, MA Port Stephens, NSW, Austr Edmonton, AL, Canada Saitama, Japan Hines, AK Cairns, Queensland, Austr Perth, WA, Australia Delaware County, NY

8 Research Goal Develop an integrated treatment system that can effectively separate the organics from MSW and convert it into biogas energy and compost.

9 Integrated RDR-APS-Digester System Trommel screen MSW Rotating Drum Reactor Biogas Energy To landfill or recycling Anaerobic Digestion Composting

10 Research Objectives Characterize the organic materials derived from MSW via Rotating Drum Reactor process Determine the biogas production potential of the organic materials and analyze the feasibility for use as feedstock for anaerobic digestion.

11 Research Approach Survey six facilities in US that use RDR process for treating municipal solid waste MSW types and amount RDR specifications and operating conditions Sample and analyze the organic materials produced from the RDR for physical and chemical characteristics Bulk density, moisture content, solids content, and nutrient and metal contents Perform batch anaerobic digestion tests to determine the rate of digestion and biogas and methane yields of organic samples.

12 VISITED MSW TREATMENT PLANTS

13 PARAMETER AZ MA NY SD TN GA Type of waste Capacity (ton/d) Organics recovered (% of MSW) Moisture content in drum (%) Max Temperature in drum ( C) Retention in drum (d) MSW Biosolids (BS) Paper & cardboard 20MSW+10 BS 10 P&C +10 BS MSW Biosolids Yard waste MSW 7.5 BS and YW MSW Biosolids 100 MSW 30 BS (16% TS) MSW Biosolids 220 MSW 9 BS (8% TS) MSW Biosolids 225 MSW 55 BS (18% TS) MSW Biosolids 200 MSW 60 BS (20% TS) Number of drums Rotation speed (rpm) Aeration in drum Yes No Yes Yes Yes Yes Openings, primary screening (mm)

15 Characteristics of Organics Recovered from MSW via RDR Process RDR Facility TS (%) MC (%) VS (%) VS/TS C (%) N (%) C/N AZ Average St. dev MA Average St. dev NY Average St. dev SD Average St. dev TN Average St. dev GA Average St. dev TS-total solids, MC-moisture content, VS-volatile solids, C-carbon, N-Nitrogen

16 Batch Anaerobic Digestion Tests Anaerobic Reactors 0.5 L working volume and 1.0 L total volume Inoculum Thermophilic Anaerobic Sludge from a working digester Test Conditions Initial volatile solids loading: 3 gvs/l Temperature: 55+2 C Digestion time: 20 days Measurements and Results Daily biogas yield (ml/gvs.day) and cumulative biogas yield (ml/gvs) Biogas composition (% methane and carbon dioxide) Initial and final ph in the reactor

17 Dairy Biogas Production and Biogas Yield During Batch Thermophilic Digestion

18 Methane Content of Biogas Produced During Batch Anaerobic Digestion

19 Biogas Yields of Organics Recovered from MSW via RDR Process RDR Facility Biogas Yield (ml/gvs) 13 d 20 d Methane Content of Biogas (%) AZ MA NY SD TN GA Average St. dev Average St. dev Average St. dev Average St. dev Average St. dev Average St. dev. 9 12

20 Conclusions The organic materials recovered from MSW using the RDR process have 44-60% moisture content, high organic content, 70-89% volatile solids in total solids, and C/N. They are highly digestible with relatively high biogas yields, ml/gvs or m 3 /kgvs. The biogas contained 58-60% methane. The organic materials derived from RDR process are suitable feedstock for anaerobic digesters.

21 Pilot Testing Planned for Anaerobic Digestion of Municipal Organic Solids Wastes at UC Davis

22 Acknowledgement Funding support from California Integrated Waste Management Board Cooperation of six MSW treatment plants

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