Biogas typically refers to a mixture of different gases produced by the decomposition of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. Biogas is a renewable energy source. The biogas can be produced by anaerobic digestion anaerobic organisms, digesting the material in a closed system, or fermentation of biodegradable materials.
Biogas can be compressed, just as natural gas is compressed to CNG, and is used to power motor vehicles. In the United Kingdom, for example, it is estimated that biogas has the potential to replace about 17% of vehicle fuel. It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards when converted to bio-methane. Biogas is considered a renewable resource because its cycle of production and use is continuous and does not generate net carbon dioxide. The organic material is grown, converted and used and then re-grown in a continuously repetitive cycle. From a perspective carbon, both carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as released when the material is finally converted into energy.
Biogas is produced by a process known as anaerobic digestion. It is a process by which organic matter is decomposed by microbiological activity and, as its name indicates, is a process that takes place in the absence of air. It is a phenomenon that occurs naturally in the bottom of ponds and marshes and gives rise to marsh gas or methane, which is a combustible gas.
There are two common human technologies for producing biogas, the first (which is more extended) is the fermentation of human waste and / or animals in digesters specially designed. The second is a technology recently developed to capture methane from municipal landfills. The scale of simple biogas plants can range from a small domestic system to large commercial plants of several thousand cubic meters. Large commercial digesters (ie fed animal faeces livestock farms) are typically much more efficient than domestic digesters, as the cow manure (and similar animals) contains more volatile solids humans. Furthermore, there is the question of small amount of feces, and plant material available in domestic systems, which means that less gas is produced, making it a less obvious method for certain purposes as producing electricity.