Produced by the action of bacteria on organic material such as manure or food remnants in airless conditions, the concept is simple. Through Heifer and other groups like the Netherlands Development Organization (SNV), families in rural areas learn how to build and install the four basic components of an underground bio-gas plant: the inlet, the digester, the gas holder and the outlet. The inlet is where families deposit manure or any organic waste (like food scraps). The digester, which can be a dome-shaped structure made of brick attached to the inlet, is an airtight chamber where bacteria decomposes the manure until it separates, becoming bio-gas and organic compost (slurry). The gas holder, as the name implies, receives bio-gas before it is released through tubes for lighting, heating and cooking. The outlet carries the slurry to a compost area, where it can be extracted and used on crops.
Consider for a moment that 2 billion people around the globe rely solely on traditional fuels for heating and cooking needs, according to the United Nations Development Programme. These fuel sources produce lots of smoke, and can harm lungs and eyes. Using bio-gas for cooking fuel improves health because it burns clean and produces no carbon monoxide emissions.
(From: Heifer Bulletin, May/June 2007, p. 41.)