Biogas Production
Biogas is produced from the anaerobic digestion of diverse organic waste sources using various methods. The International Energy Agency describes the following in its publication Biogas Production and Utilisation (PDF 1.6 MB) (Download Adobe Reader):
Sources
- Sewage sludge
- Agricultural wastes
- Industrial wastes
- Animal by-products
- Municipal solid wastes
Anaerobic Digestion Methods
- Dry continuous digestion of source separated waste
- Farm-scale biogas production
- Large-scale centralized co-digestion
Landfills are a large source of biogas.
In a landfill, anaerobic digestion of wastes occurs naturally. Gas collection is practical for landfills that are at least 40 feet deep and contain at least 1 million tons of waste. The Oregon Department of Renewable Resources provides an overview of biogas production technologies.
After biogas is produced and extracted, it must be upgraded for pipeline distribution or use as a vehicle fuel. This means increasing the proportion of methane and decreasing the proportion of carbon dioxide and contaminants. This is accomplished using processes such as absorption, adsorption, membrane separation, and cryogenic separation. For information on upgrading biogas, see Biogas Upgrading to Vehicle Fuel Standards and Grid Injection (PDF 284 KB). Download Adobe Reader.
The International Energy Agency estimates that, in 2005, 185 anaerobic digestion plants had the capacity to process 5 million metric tons of municipal solid and organic industrial waste to generate 600 MW of electricity. The potential for biogas production is much larger. A report by the CIVITAS Initiative estimates that European biogas production could satisfy 12-20% of European natural gas consumption.
Natural Gas Vehicles for America cites a 1998 study estimating that the biogas potential from landfills, animal waste, and sewage is equivalent to 6% of U.S. natural gas consumption or 10 billion gasoline gallon equivalents of transportation fuel (about 7% of year 2006 U.S. gasoline consumption). See Sequestering Greenhouse Gases from Landfills, Animal Waste, Sewage, and Other Sources Via Biomethane Production (PDF 28 KB). For a map of actual and potential U.S. landfill gas sites, see Landfill Gas Energy Projects and Candidate Landfills (PDF 199 KB). Download Adobe Reader.