Biogas is naturally produced when any organic matter decomposes under anaerobic conditions (in the absence of oxygen). The gas consists mainly of methane (CH4) and carbon dioxide (CO2) in approximately 3:2 ratio. Methane is the important component as it is a highly flammable gas that can be utilized as fuel for cooking, lighting, water heaters and, if the sulphur is removed, it can be used to run biogas-fuelled generators to produce electricity.
Biogas can be produced under controlled circumstances in specially designed biogas digesters. There are many types of digesters that are being used throughout the world. In countries such as Germany, biogas technology is highly advanced and applied primarily to produce green electricity in the megawatt range. In other developing countries such as India and China a more basic technology is used to provide energy primarily for cooking purposes.
India for instance, has more than a million digesters producing all the cooking energy for thousands of villages using human (sewerage) and animal (manure) waste in the process. One of the major spin-offs of using a biogas digester is that the spent material is in the form of organic compost that can then be used to increase the yield of planted crops.