Anaerobic digestion is the process by which organic matter such as animal or food waste is broken down to produce biogas and bio-fertilizer. This process happens in the absence of oxygen in a sealed, oxygen-free tank called an anaerobic digester. Biogas is primarily methane (CH4) and carbon dioxide (CO2) and hydrogen sulphide (H2S), moisture and siloxanes.
The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.