Bio-gas is a mixture containing 55 to 60 percent carbon dioxide and the rest being impurities H2, H2S and some N2, can be produced from the decomposition of animal, plant and human waste. It is clean but slow burning gas and usually has a calorific value between 21000 KJ/ KG. It can be used directly in cooking thereby the demand for firewood. Moreover, the material from which the bio-gas is produced retains its value as a fertilizer and can be returned to the soil. Bio-gas has been popularly called GOBAR gas, because cow dung has been the material for its production. The piggery waste as well as poultry droppings can also be used for bio-gas generation. A few other materials through which biogas can he generated are algae, crop residue,
kitchen waste, paper waste and waste sugarcane refinery, water hyacinth etc. Any cellulose organic material of animal or plant origin which is easily biodegradable is a potential raw material suitable for bio-gas production.
Bio-gas is produced by digestion. pyrolysis or hydro gasification. Digestion is a biological process that occurs in the absence of oxygen and in the presence anaerobic organisms at ambient pressure and at temperatures between 35-70 degrees Centigrade. The container in which this digestion known as the digester.