Lesson 8 of 11 · 7 min
Biogas
NCERT §8.4
Saturday: Ananya takes the bus to her uncle's village. Behind the cowshed is a round concrete tank sunk 12 feet into the ground, and a pipe runs from it into the kitchen.
The lesson in notes
In short
Biogas is a mixture of gases, mostly methane, made by microbial activity and usable as fuel.
The gas a microbe produces depends on the microbe and its substrate. In dough, cheese and beverages the main gas is CO₂.
Some bacteria that grow anaerobically on cellulosic material make large amounts of methane along with CO₂ and H₂. They are called methanogens; Methanobacterium is a common one.
Methanogens live in the anaerobic sludge of sewage treatment and in the rumen (a part of the stomach) of cattle, where they help break down cellulose and so support the animal's nutrition.
Cattle dung (gobar) is therefore rich in methanogens and can be used to generate biogas, called gobar gas.
A biogas plant has a concrete tank 10-15 feet deep into which bio-wastes and a slurry of dung are fed. A floating cover over the slurry rises as microbes produce gas.
One outlet pipes the gas to nearby houses for cooking and lighting; another removes the spent slurry, which can be used as fertiliser.
Biogas plants are built mostly in rural areas, where cattle dung is plentiful. The technology was developed in India mainly through the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).