Microbes and biogas

Biogas is a mixture of gases, mainly methane, made by microbial activity. It burns cleanly and is used as a fuel.

It is made by bacteria called methanogens, such as Methanobacterium, which grow anaerobically (without oxygen) on cellulose-rich material, producing methane along with CO₂ and hydrogen.

Methanogens live in two notable places:

• In the anaerobic sludge of sewage treatment plants.
• In the rumen, a part of the stomach of cattle. There they help break down the cellulose in grass and fodder, which matters a great deal to the animal's nutrition. Cows themselves cannot digest cellulose.

So cattle dung, gobar, is rich in these bacteria, and can be used to make biogas, often called gobar gas.

A biogas plant:

• A concrete tank, 10-15 feet deep, is filled with a slurry of dung and water.
• A floating cover sits on top. As the bacteria produce gas, the cover rises.
• An outlet pipe carries the gas to nearby houses for cooking and lighting.
• Another outlet removes the spent slurry, which is a good fertiliser.

Biogas plants are built mostly in villages, where cattle dung is plentiful. The technology in India was developed mainly by the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).