Biogas an important renewable energy source
a World Bioenergy Association fact sheet, May 2013
“Biogas” is a gas produced by anaerobic fermentation of different forms of organic matter and is composed mainly of methane (CH4) and carbon dioxide (CO2). Typical feedstocks for biogas production are manure and sewage, residues of crop production (i.e., straw), the organic fraction of the waste from households and industry, as well as energy crops including maize and grass silage. Biogas is supplied to a variety of uses or markets, including electricity, heat and transportation fuels. In many countries using the gas for direct combustion in household stoves and gas lamps is increasingly common, producing electricity from biogas is still relatively rare in most developing countries. In industrialized countries, power generation is the main purpose of most biogas plants; conversion of biogas to electricity has become a standard technology. To improve overall efficiency of biogas utilisation, combined heat and power plants are often used, with part of the heat utilised for maintaining reactor temperature and sometimes for heat treatment of the incoming material. A biogas plant on a farm, for example, has a number of different elements, such as the liquid manure store, the receiving and mixing area, the digester or reactor, the gas storage tank and storage for digester residue. In the case of a combined heat and power (CHP) application, there also needs to be grid connection for the electricity and a connection to the heat user.