Biogas is a combustible gas produced when organic matter such as crop waste is broken down without oxygen.
This oxygen-free process is called anaerobic digestion. Microorganisms decompose materials including animal manure, sewage sludge, food waste, and agricultural residues. The resulting gas is usually rich in methane, with carbon dioxide and small quantities of other gases also present.
Biogas can be burned in boilers, engines, or combined heat-and-power systems. After cleaning to remove carbon dioxide, hydrogen sulfide, water, and other impurities, it can become biomethane, a fuel suitable for injection into some natural-gas networks or use in vehicles.
Biogas is not the same as biodiesel or ethanol. Biodiesel is made from oils or fats, while ethanol is an alcohol commonly produced by fermenting sugars or starches. The climate benefits of biogas depend on feedstock, leakage control, processing energy, and how the waste would otherwise have been managed.