The biogas plant works on the principle of anaerobic digestion, which is the fermentation, in the absence of air, of organic material such as human, animal and agricultural waste. During fermentation, these wastes produce a gas consisting of 50-70% methane and the remaining slurry forms an organic, high quality manure. In rural communities of developing countries, animal excreta and crop stalks, which were burned for fuel, can be recycled as fertilizer to improve soil quality and raise crop yields. The by-product, methane gas, can be supplied constantly as a fuel. The biogas plant is also an effective way of dealing with excreta and thus improving the hygiene and standard of health. (Governor of Osaka Prefecture Prize in the 2nd International Design Competition, Osaka in 1985.)