Using gas (principally methane) given off when vegetative matter breaks down, as fuel for stoves, engines or lighting.
Most biogas digesters are metal or cement tanks with a heavy floating top which pressurizes the gas. The "Chinese type" has a fixed top. In India, biogas is often called gobar gas.
UN Development Fund for Women (UNIFEM), the Yemeni Ministry of Energy and Minerals, and other organizations set up a pilot project to build biogas digesters, pit latrines and improved drainage for the animal sheds in the Yemeni village of Al-Habeel. Animal dung was channelled into 22 biodigesters, cleaning up the unhealthy wastes from the area, and generated a reliable supply of gas which can be burned free of cost and smoke, providing 85% of the energy needs of the household's connected to the system. Biogas production also cleaned the environment of unhealthy wastes, lessened the depletion of trees, and freed women from the burden of gathering fuelwood. The organic residues removed from the biodigesters are a rich fertilizer and applied to crops instead of expensive chemicals, and their application has led to a 25% increase in food grain and vegetable production.