Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel. Microbes produce different types of gaseous end products during growth and metabolism. The type of a gas produced depends upon the microbes and the organic substrates they utilise. In the examples cited in relation to fermentation of dough, chees making and production of beverage, the main gas produced was `CO_2`. However certain bacteria which grow anaerobically on cellulose material, produce large amount of methane along with `CO_2` and `H_2` . These bacteria are collectively called methanogens and one such common bacterium is Methano-bacterium. These bacteria are present in the rumen part of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Thus the excreta (dung) of cattle is called Gobar also. They possess high level of these bacteria. Dung can be used for generation of biogas commonly called gobar gas. The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry. Which keeps on rising as the gas is produced in the tank due to the microbial activity.
The biogas plant has an outlet which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertilisers Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes. The biogas thus produced is used for cooking and lighting. The technology of biogas production was developed in India mainly due to efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).
