The Biogas is produced by a process known as anaerobic digestion. This is the slow natural reaction caused by the anaerobic bacteria present in biodegradable materials such as food waste, raw sewage, plant material, and crops. The Biogas is mainly composed of methane(CH4) and carbon dioxide (CO2). There may also be trace amounts of hydrogen sulphide (H2S) and  siloxanes. The resultant gases can be can be combusted or combined with oxygen, ( oxidized )  releasing energy which can then be used to drive a turbine to generate electricity or heat.