India's low-tech energy success.

• Author: Sampat, Payal

How 2 million power plants are turning cow dung into electric power and cooking fuel - and ending up with even better fertilizer than manure.

Cow dung may not be the first thing that comes to mind when you think of state-of-the-art energy technology. Yet in the tiny village of Pura in south India, this humble waste material is providing people with basic amenities formerly in short supply: electric light, pumped water, and clean cooking fuel. An ingeniously simple process that converts dung into a flammable gas, called biogas, has greatly improved daily life for Pura's 485 inhabitants - and for over 10 million other rural Indians.

Biogas, as its name suggests, is produced by extracting chemical energy from organic materials. This process takes place in a sealed container known as a biogas digester. The digester is usually a squat, cement cylinder two to four meters in diameter, with a duct in the side that allows the dung or other organic wastes to be fed in, along with water. In ambient temperatures of 25 to 35 degrees centigrade, the material soon begins to ferment. This produces a mixture of gases, primarily methane and carbon dioxide, and a nutrient-rich slurry. The gas is drawn out through a valve at the top of the digester, and the slurry is drained off into settling troughs at its base. [ILLUSTRATION OMITTED].

Methane is the combustible component of biogas. It is piped into homes to be used as a cooking fuel, or used to fire a diesel engine to generate electricity, as in the case of Pura. The slurry is such an excellent fertilizer that it's often more highly valued than the gas - biogas plants are often called "biofertilizer plants."

Biogas dates as far back as the 16th century, when it was used for heating bath-water in Persia, and it has been used in India for almost a hundred years. In 1981, however, the Indian government launched biogas production on a large scale, by embarking on a "National Project on Biogas Development." Close to 2 million digesters have been constructed in India since then, and although the program has had its share of problems, it has made substantial progress. Most plants are located in rural, agrarian parts of the country and are designed to serve the cooking needs of a single household of four to seven people. Over 1,150 large "community" plants - like the one in Pura - have also been installed. These are operated by an entire village, and the cooking fuel or electricity is shared by the community.

WHY BIOGAS?

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