Everything about biogas

Biogas typically refers to methaneproduced by the fermentation of organic matter including manure, wastewater sludge, or municipal solid waste, under anaerobic conditions. The process is popular for treating many types of organic waste because it provides a convenient way of turning waste into electricity, decreasing the amount of waste to be disposed of, and of destroying disease causing pathogens which can exist in the waste stream. The use of biogas is encouraged because methane burns with a clean flame and produces little pollution. The digestion has three main stages. The first, hydrolysis, involves breaking down the large macromolecules to sugars, amino acids, and fatty acids by bacteria under aerobic conditions. The second stage is acetogenesis, during which acetogenicbacteria convert sugars into short-chain acids, mainly acetic acid. The third stage is methanogenesis, which is carried out by anaerobic bacteria. Here, the acids are converted into methane. Other sources of biogas are landfills, anaerobic lagoons and sewage treatmentplants. Biogas from municipal sewage treatment plants typically contains 55% to 65% methane, with the remainder being primarily carbon dioxide. In addition it can contain up to 0.5% Hydrogen Sulfide, and is generally saturated with water, giving it a corrosive nature. Since the anaerobic digestion process requires a a constant temperature of up to 95 degrees F (Mesophilic process) or 135 degrees F (Thermophilic process), part of the biogas generated is usually used to heat the digester. The remainder can be used to generate steam or electicity via engine generators, gas turbines, or microturbines. Excess gas, due to fluctuations in the production rate, is generally flared. Biogas from landfills tends to have lower methane percentages due to the less homogeneous nature of the waste, as well as the lack of ability to optomize the digestion process. Waste from food processing plants and breweries tends to have a higher methane content. One major benefit producing and burning biogas is that emissions are captured and treated from the inevitable decomposition of the organic matter. Ammonia and methane are released to the atmosphere during desomposition in landfills or during composting. The digester accelerates decomposition and enhances methane production and capture. See anaerobic digestion. Biogas can have a higher heating value in the range of 150 to 650 Btu/scf (6 to 24 MJ/m³), which is about half that of natural gas. The medium-heat gas can be fired in a number of prime movers for power generation (mechanical, thermal, or electrical). The energy produced is considered renewable energy.