Microbes usually produce gases during their growth and metabolism. Based on the organic substrates they utilise, different microbes produce different gases. Methanogens produce copious amounts of methane along with carbon dioxide and hydrogen gases from organic matter such as cellulose. Methanobacterium present inside the rumen of cattle digest the cellulose present in grass, and its dung is rich in the same bacteria. The dung or gobar is used to generate biogas in a biogas plant.
A biogas plant is an effective way to generate energy from wastes through microbial activity. Biogas generated from biogas plants can be used as low-cost fuel that burns without emitting smoke, for lighting streetlights and to run electric engines. The technology of biogas production was developed in India by the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).
In India, the fixed-dome type and the floating gas holder types are used. In the fixed-dome type, the dome is made of concrete and is fixed whereas in the floating gas holder type, the lid is made of stainless steel and is movable. The floating gas holder type of biogas plant is covered with a floating lid so that it can freely rise when methanogens produces gas inside the biogas plant. The bio-wastes and cattle dung in the slurry are first soaked in water and mixed in the mixing tank and then allowed into the main tank. Methanobacterium and other anaerobic bacteria present in the slurry decompose it to release a mixture of gases such as methane, carbon dioxide and hydrogen, known as biogas. The remaining slurry is used as fertiliser.