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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Organics: Anaerobic Digestion
Co-Digestion

Co-digestion is a process whereby energy-rich organic waste materials (e.g. Fats, Oils, and Grease (FOG) and/or food scraps) are added to dairy or wastewater digesters with excess capacity. In addition to diverting food waste and FOG from landfills and the public sewer lines, these high-energy materials have at least three times the methane production potential (e.g. biogas) of biosolids and manure.

A primary benefit of co-digestion is that it uses existing infrastructure and expertise to divert food waste and FOG for the purpose of biogas production. In California alone there are almost 140 wastewater treatment facilities that utilize anaerobic digesters, with an estimated excess capacity of 15-30%. Other benefits include greenhouse gas emission reductions, economic benefits and diversion opportunities.

EPA Grant Funds Research Project on Anaerobic Digestion at East Bay Municipal Utility District (EBMUD)

To further study co-digestion, in 2006 the EPA awarded a $50,000 grant to East Bay Municipal Utility District in Oakland, CA to investigate the benefits and limitations of anaerobically digesting food scraps in a wastewater digester. Food scraps were sourced from restaurants, grocery stores, and other food handling facilities in the San Francisco Bay Area. EBMUD bench-scale digesters were fed only food wastes, but were operated under a variety of conditions, varying digester loading rates, temperature, and other parameters. EBMUD processed 40 tons of post-consumer food per day in anaerobic digesters that break down sewage sludge, which in turn reduced greenhouse gas emissions, generated renewable energy, produced a soil amendment, and recycled the largest single component of urban municipal solid waste: organic waste.

The final report of the project and a fact sheet summarizing the results:

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