Write a note on biogas.
ANS:
* Biogas is produced by the decay of biomass and it consists of 65-75% methane, 30-40% carbon dioxide as well as traces of H2,H2S, and N2.
* Because biogas is generally obtained from the solid wastes of animal dung, sewage, crop residues, agro-wastes and poultry droppings, it is traditionally called 'Gobar gas'.
* Methane is an excellent fuel. The calorific value of biogas is 35-40 kJ/g.
* Two types of biogas plants are commonly used in India.They are :
1. Fixed-Dome Type
2. Floating Gas-Holder Type
* The floating gas-holder type plants have been prepared by the Khadi and Village Industries Commission (KVIC) and are used where biogas is obtained from the animal dung. It consists of a dome like structure, made of steel, that floats up as the pressure of biogas evolved increases.
* The fixed-dome type structure has a longer life. Its dome can be made from bricks. Thus, the cost of the plant is reduced. This type of plant is more suitable for obtaining biogas from human excreta and other bio-wastes.
* PROCESS:
o A slurry of dung, other biowastes and water is prepared in a mixing tank.
o This slurry is fed into the digester which is a closed underground tank made of bricks.
o The digester is sealed from the top.
o The anaerobic micro-organisms decompose the biomass in the digester and produce biogas which is a mixture of fuel gases like methane, hydrogen, hydrogen sulphide with carbon dioxide and nitrogen.
o After a few days, sufficient gas is produced which is supplied to the places of use.
* ADVANTAGES:
1. It can be supplied to the consumers through pipes.
2. Its main component methane is an excellent fuel and burns without smoke.
3. It does not produce ash during burning.
4. It can be used as a fuel for domestic heating, cooking, lighting as well as to generate electricity.
5. It can be supplied to industries as a fuel.
6. The slurry left behind in the digester serves as an excellent manure for farmers.
7. It provides us with a scientific method of disposal of organic wastes.
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