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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Digestion Process for Converting Agricultural Byproducts, and Municipal Solid Wastes into Bioenergy

Location: Bioproducts Research

2012 Annual Report

1a. Objectives (from AD-416):
The main objective of this joint project is to investigate biomethane production from agricultural waste, fish waste and other municipal solid wastes. Monterey County produces $3 billion worth of vegetable produce annually and up to $100 million in fishery products; the waste from these industries are presently landfilled at a high cost in both monetary and environmental terms. The team will study optimal handling of this material to produce biomethane including development of the USDA’s anaerobic basin system (patent application pending) at the Salinas landfill site. This system is designed to allow for maximum retention time and near theoretical biomethane production. The system must be located at a landfill to handle most solid wastes, especially fish, and agriculturally-derived biomass wastes. The USDA and SVSWA intend to develop a demonstration facility to validate the impacts of using local waste as a feedstock for bioenergy conversion to improve the local rural economy.

1b. Approach (from AD-416):
Research is needed beyond the laboratory scale to validate anaerobic conversion of agricultural byproducts, fish waste, and municipal solids waste at a demonstration scale; research that is best accomplished at a landfill environment because of permitting, the volumes of waste required, and other practical applications. Two test basins will be constructed with the capacity to accept 8 tons of wet waste materials which will be fermented over a 30-90 day time period. Fermentation will be performed under high solids conditions and biogas will evolve. Test basins are critical for confirming theories of hydraulic conveyance of waste materials and semi-continuous introduction of slurried materials to a hermetically sealed and co-currently fermenting basin. Total retention time at this larger scale will help indicate the throughput capacity of a basin system. Several repetitions of the basin system will test design hypotheses for reuse of water, excavation of solid residuals, and optimal system operation. In order to test the validity of the USDA anaerobic conversion system (the USDA “basins”), the process must be tested at larger scale, with the following hypotheses: Hypothesis 1: The feed mechanism, with its hermetic sealing, can be adequately designed to allow filling of the basin without disrupting bioreaction. Hypothesis 2: Material can be successfully conveyed from the feedbox to the basin floor via hydraulics and gravity. Hypothesis 3: Complete biological stabilization of the organic waste streams can be achieved with adequate retention time and moisture content at large scale. Hypothesis 4: Complete degradation of biodegradable volatile solids can be achieved at realistic retention time under high solids conditions at large scale. Hypothesis 5: Biogas can be produced and efficiently collected without loss to the atmosphere. Hypothesis 6: Enhanced biogas yields can be achieved with extended retention time. Hypothesis 7: Agricultural (cellulosic biomass and manure), fish wastes (a source of nitrogen) and municipal wastes (waste activated sludge) can be easily incorporated into the anaerobic basins via commingled feedstocks.

3. Progress Report:
This research is developed in support of Objective 3 of the parent project plan, and supports the milestone for 18-24 months related to anaerobic digestion. Specifically it is in line with Objective 3; to develop pretreatment technologies that enable commercially-viable* biorefineries capable of utilizing diverse feedstocks such as rice straw, wheat straw, commingled wastes (including MSW), sorghum, switchgrass, algae, and food processing by-products. Within the next quarter, a pilot-scale anaerobic digestor will be established in Salinas at the Crazy Horse Landfill, to be used by both parties for their joint work in California. Plans are for this system to be ready in early fall (September-October, 2012), with testing at larger scale to be implemented over the next year. Salinas, CA is exploring the viability of bioenergy production from waste sources encountered in the U.S. at a large scale, with operation plans for as much as 100 tons per day. This system, along with lab-scale tests, provides important data for domestic application at a municipal scale.

4. Accomplishments

Last Modified: 10/19/2017
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