What is biomass ? Explain the principle and working of a biogas plant using a labelled schematic diagram.

Explanation

The material contained from the bodies of plants and animals is called biomass. It includes wastes from tree and grass, crops, forest, agricultural and urban wastes. The excreta of living organisms and their bodies after death also contribute to the biomass. It acts as a fuel. It is a mixture of methane `(CH)_4` carbon dioxide `(CO_2)`, hydrogen `(H_2)` and hydrogen sulphide `(H_2S)`. So, the chief constituent of biogas is methane (65%).
Principle : Biogas is produced as a result of anaerobic fermentation of biomass in the presence of water.
Construction of Biogas Plant: The biogas plant is a brick and cement structure having the following five sections :
(i) Mixing tank : It is present above the ground level.
(ii) Inlet chamber : The mixing tank opens underground into a sloping inlet chamber.
(iii) Digester: The inlet chamber opens from below into the digester which is a huge tank with a dome-like ceiling. The ceiling of the digester has an outlet with a valve for the supply of biogas.
(iv) Outlet chamber : The digester opens from below into an outlet chamber.
(vi) Overflow tank : The outlet chamber opens from the top into a small overflow tank.

Working of Biogas Plant
(i) A mixture of farm waste is fed into the biogas plant. This waste is mixed to make slurry.
(ii) Slurry is then fed into the digester. Digester is an air-tight chamber and oxygen is not present in it.
(iii) Anaerobic bacteria in digester carry out decomposition of slurry. This results in production of biogas.
(iv) Biogas is sent out through an outlet so that it can be suitably used.
(v) Decomposed matter is taken out and it can be used as manure.