Biogas refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced normally in Landfill sites or in Water Treatment Plants, from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. Biogas is produced by anaerobic digestion with methanogen or anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials. This closed system is called an anaerobic digester, biodigester or a bioreactor.
Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes. The release of unburnt methane to the atmosphere has an estimated greenhouse effect to be 104 times more powerful than the release of CO2. This energy release allows biogas to be used as a fuel to be used in a gas engine to convert the energy in the gas into electricity and heat. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. Biogas is a renewable resource because its production-and-use cycle is continuous.