The bio-gas is obtained from plant, animal and human waste, also called as biomass. The main source of biogas is wet cow dung, which is most commonly used for production of biogas. The other sources of biogas are: sewage, crop residue, vegetable wastes, waste wood, dry leaves of the plants, broken branches of trees, garbage, waste paper, poultry droppings, pig manures, algae, ocean kelp etc.