Explain the working of a Biogas plant.

Explanation

(i) Biogas is a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural wastes manure, municipal wastes, plant material, sewage, food waste etc.
(ii) The excreta of cattle called dung is commonly called "Gobar". Gobar gas is generated by the anaerobic decomposition of cattle dung. It consists of methane, `CO_(2)` with some hydrogen, nitrogen and other gases in trace amounts.
(iii) In a biogas plant, anaerobic digestion is carried out in an air tight cylindrical tank known as digester (Fig). It is made up of concrete bricks and cement or steel. Bio-wastes are collected and slurry of dung is fed into this digester. It has a side opening into which organic materials for digestion are incorporated for microbial activity. Anaerobic digestion is accomplished in three stages, solubilisation, acidogenesis and methanogensis. The outlet is connected to a pipe to supply biogas. The slurry is drained through another outlet and is used as fertilizer. Biogas is used for cooking and lighting.