2013 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.
The Methane Digester Project was co-funded by the Salinas Valley Solid Waste Authority and the USDA through the SCA 58-5325-1-477. The basin design configuration was produced and installed by ARS scientists. Establishment of the anaerobic culture is slated to occur in the month of August 2013 and proof of concept will continue throughout the fall and winter terms. Successful demonstration of the process will enable the commercialization of the basin concept coinciding with the scale-up of the Salinas commercial scale autoclave project. Demonstration of the basin concept has broad application related to compliance with California Assembly Bill 341 (75 % landfill diversion by 2020) and optimizing the utilization of farm wastes, food processing streams, and source separated organic wastes. Stakeholder interest is broad ranging from waste handlers to municipalities, farmers, and technology partners. This research addresses parent project objective 1: "Develop enzyme-based technologies (based on cleaving specific covalent crosslinks which underlie plant cell wall recalcitrance) thereby enabling new commercially-viable* saccharification processes".