Microbes in the
production of biogas (Gobar gas)
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., Biogas is produced under
anaerobic condition, when the organic materials are converted through
microbiological reactions into gas and organic fertilizer. Biogas primarily
consists of methane (63 percent), along with CO2 and hydrogen. Methane
producing bacteria are called methanogens and one such common bacterium
is Methanobacterium. Biogas is devoid of smell and burns with a blue
flame without smoke. The Methanogens are also present in anaerobic
sludge and rumen of cattle.
In rumen, these bacteria help in the breakdown
of cellulose. 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, CO2 with some hydrogen,nitrogen and other gases in trace
amounts.
In a biogas plant, anaerobic digestion is carried
out in an air tight cylindrical tank known as digester (Fig. 9.4). 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 methanogenisis. 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. The technology of biogas production
was developed in India mainly due to the efforts of Indian Agricultural
Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).
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