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Biogas, a cheap secondary renewable energy, is a gaseous fuel obtained from biomass by the process of anaerobic digestion or fermentation. Biogas fermentation is the process by which organic materials such as human or animal excreta, domestic wastage, agricultural wastage etc, are degraded, by huge quantities of various microbes of different functions, under anaerobic conditions, to yield methane (about 55-70% content), carbon dioxide (about 30-45% content) and low amount of other gases in the end. Biogas can be used as a vehicle fuel or for generating electricity. It can also be burned directly for cooking, heating, lighting, process heat and absorption refrigeration. Cattle dung, agricultural residue, poultry dropping, water hyacinth, human excreta may be used as raw materials for biogas plants. A typical biogas plant consists of a digester in which the slurry (dung mixed with water) is fermented; an inlet tank used to mix the feed and let it into the digester; a gas holder/ dome in which the generated gas is collected; an outlet tank to remove the spent slurry; distribution pipelines to take the gas into the kitchen.