Anaerobic Digestion Resources
If 50 percent of the food waste generated each year in the U.S. was anaerobically digested, enough electricity would be generated to power 2.5 million homes for a year. By anaerobically digesting food waste, two valuable products, renewable energy and soil amendment, can be generated.
What is Anaerobic Digestion?
Anaerobic digestion is a process where microorganisms break down organic materials, such as food scraps, manure, and sewage sludge, in the absence of oxygen. Recycling food waste through anaerobic digestion produces biogas and a soil amendment, two valuable products.
Biogas, made primarily of methane and carbon dioxide, can be used as a source of energy similar to natural gas. The solid residual should be land applied or composted and used as a soil amendment.
Food can either be digested at facilities specifically designed for the organic portion of municipal solid waste, or co-digested at wastewater treatment plants and manure digesters. Co-digestion is a process whereby additional, energy-rich organic materials (e.g. food scraps or fats, oils, and grease) are added to dairy or wastewater digesters with excess capacity. Co-digestion uses existing infrastructure to divert food scraps and fats, oil, and grease. Some haulers charge less if the food waste is separated from the trash and sent for anaerobic digestion rather than landfilling.
The two main types of anaerobic digesters are low-solids and high-solids (dry fermentation) and are based on the percent solids of the material being digested. Low-solids digesters generally process materials with less than 15 percent solids and are common at wastewater treatment plants and manure digesters. High-solids digesters are common in Europe and becoming more common in the United States.
Anaerobic Digestion Success Stories
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- Purdue University turns food waste into renewable energy by partnering with the City of West Lafayette to send food waste to the local wastewater treatment plant. At the wastewater treatment plant, the food is added to the anaerobic digester, where it is processed by microbes to generate biogas, a source of renewable energy, and a solid residual that can be used as a soil amendment. Learn more (PDF) (17 pp, 3.3 MB)
- The University of Wisconsin Oshkosh started turning organic materials into renewable energy in fall 2011 with a dry fermentation anaerobic digester. The first of its kind in the nation, this facility uses agricultural plant waste, City of Oshkosh yard waste, and campus-generated food waste to produce biogas. The digester produces enough energy to power up to 10 percent of the 13,500-student institution.
- East Bay Municipal Utility District (EBMUD) in Oakland, CA was the first wastewater treatment plant in the nation to convert post-consumer food scraps to energy via anaerobic digestion. Waste haulers collect post-consumer food waste from local restaurants and markets and take it to EBMUD. In an anaerobic digester, bacteria break down the food waste and release methane as a byproduct. EBMUD then captures the methane and uses it as a renewable source of energy to power the treatment plant. After the digestion process, the leftover material can be composted and used as a natural fertilizer. Learn more