Masters Thesis

Food waste diversion and utilization in Humboldt County

This thesis investigates the feasibility of establishing a regional food waste digester facility in Humboldt County. California state law AB 939 mandates that all jurisdictions divert 50% of their waste stream away from the landfills. Although successful recycling and green waste composting programs have been developed in the County, some cities have yet to reach the diversion target. The largest component of the remaining disposed waste stream is food waste (~20%). For the purpose of establishing a food waste diversion program, the economics and environmental impacts of a food waste digester was compared to in-vessel composting as an alternative to hauling waste to the landfill. The results of the analysis indicate that establishing either alternative will reduce the overall cost of waste management by $12 to $16 million over a 20 year time horizon. The anaerobic digestion alternative has the lowest life cycle cost, due in large part to the renewable energy generation potential of anaerobic digester systems. Over time, as energy prices rise, composting and long-distance waste hauling strategies will become more expensive while the economics of anaerobic digestion systems improve. A regional food waste digestion facility will reduce greenhouse gas emissions in three ways: first, from avoided long-distance waste hauling (326 MTCO2e/year); second, from offset grid electricity use (540 MTCO2e/year); and third, from avoided methane emissions at landfills (average 5,000 MTCO2e/year). These reductions will help participating jurisdictions to meet future requirements for carbon emissions accounting. Establishing a food waste digester facility will contribute to the long-term sustainability of the region.

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