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Organics: Anaerobic Digestion
Anaerobic digestion is almost as old as the planet itself. It is a process that, in the absence of oxygen, converts organic carbon into carbon dioxide (CO2) and methane (CH4)-a concoction called biogas Biogas a methane rich gas produced by the anaerobic digestion of animal dung, human sewage and/or organic waste. Biogas also contains carbon dioxide., which can be used as an energy source.
The production of Biogas is one of the many benefits of anaerobic digestion.
What converts organic carbon-like organic wasteOrganic Waste Waste that is readily biodegradable, or easily breaks down with the assistance of microorganisms, e.g. materials that contain carbon-based molecules. This includes food waste, green waste, manure, putrescible waste, and grease., dairy manure, and human sewage-into biogas?
Bacteria! Lots and lots of naturally occurring bacteria break down complex organic molecules, producing CO2 and CH4 as 'waste' products.
Anaerobic Digestion treats wastewater, minimizes waste and yields energy; it is an ancient yet currently widely used technology that holds incredible promise for the future.
In recent years, there have been scientific advances towards the use of anaerobic digesters already in place at wastewater treatment plants to co-digest food waste with biosolids. There are many benefits to using the anaerobic digesters at wastewater treatment facilities to digest food waste including; existing excess capacity, on-site expertise, systems to utilize the biogas produced and a method of reducing the volume of the food waste before transporting it to compost facilities.
EPA Grant Funds Research Project on
Anaerobic Digestion at East Bay Municipal Utility District (EBMUD)
To further study this technology, in 2006 the EPA awarded a $50,000 grant to East Bay Municipal District, a wastewater treatment facility in Oakland, CA to investigate the benefits and limitations of anaerobically digesting food wastes from restaurants, grocery stores and other food handling facilities at a treatment facility. 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 waste per day in anaerobic digesters that break down sewage sludge, and in turn reduced greenhouse gas emissions, generated renewable electric power, 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:
- "Anaerobic Digestion of Food Waste" Report (PDF) (62 pp, 412K)
- Turning Food Waste into Energy at the East Bay Municipal Utility District (PDF) (2 pp, 427K)
Wastewater Treatment Facilities are particularly ideal for anaerobically digesting food waste. The technology offers climate reductions, economic benefits and diversion opportunities. Please see The Benefits of Anaerobic Digestion at Wastewater Treatment Facilities (PDF) (5 pp, 150K) fact sheet for further information.
