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Biogas fuel, typically called biogas, is a form of biofuel created by the anaerobic decomposition of organic materials. Anaerobic decomposition refers to decay that occurs with the help of microorganisms in an oxygen-free environment. Organic material is biodegradable matter from a living or once-living organism, like plants, animals, or their wastes. As the decomposition of these materials takes place, a system harnesses the resulting hydrogen, nitrogen, carbon monoxide and methane, gases which can be reacted with oxygen to create energy. Biogas fuel may be used for heating processes and, if concentrated, for vehicle transportation.
Biogas fuel is produced in a biogas plant within an airtight container called a digester. Organic wastes, such as manure, municipal waste, and plant matter, are dumped into the tank where bacteria then begins digesting it, causing its accelerated decay. To facilitate fast decomposition with optimal gas production, the tank is kept between the temperatures of 29°C and 41°C (84.2°F-105.8°F). It is best to keep the slurry in the tank at a slightly basic pH to ensure faster decomposition, as the material will tend to create more carbon dioxide, which has an acidic pH, to neutralize the mixture.
The slurry within the tank must also be occasionally stirred to prevent a hard crust from forming on top of the wastes. A crust can trap the gases within the slurry and impede the machinery’s ability to harness the gases. There are two different ways of feeding that require different types of digesters, batch feeding and continuous feeding. Batch feeding systems use mostly solid wastes added in installments, and continuous feeding models add mostly liquids to the digester. In either digester, the gas released from the decaying material is caught via a pressurized system that allows gas to flow into a drum, but does not allow gas to escape back into the digester.
Generally, biofuels are liquid, gaseous, or solid fuel made from live or recently dead organic material known as biomass, as opposed to fossil fuels, which are composed of ancient biological materials. In contrast to fossil fuels, biogas fuel is often heralded by environmentalists for its relatively small contribution to the carbon concentration in the atmosphere. Though both emit carbon, fossil fuels release carbon that has been buried for many years and, in effect, removed from the carbon cycle. Carbon released from biomass, however, has only recently been stored in the form of organic matter and is still part of the cycle. Therefore it does not cause as much of an upset in the carbon concentration in the atmosphere.
In addition to carbon output, biogas fuel is often preferred to fossil fuels because it is a low-cost, renewable source of energy, it uses otherwise wasted materials, and it may be produced in small-scale sites, making it a viable option for regions in developing nations. Biogas fuel, however, also has its critics. Some argue that food crops grown for the purposes of fuel production will create a global food shortage. Biofuels may also cause deforestation, water pollution, soil erosion, and a negative impact on oil producing nations.
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