Bio gas is made from organic waste matter after it is decomposed. The decomposition breaks down the organic matter, releasing various gases. The main gases released are methane, carbon dioxide, hydrogen and hydrogen sulphide. Bacteria carry out the decomposition or fermentation.
The conditions for creating bio gas have to be anaerobic that is without any air and in the presence of water. The organic waste matter is generally animal or cattle dung, plant wastes, etc. These waste products contain carbohydrates, proteins and fat material that are broken down by bacteria.
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The waste matter is soaked in water to give the bacteria a proper medium to grow. Absence of air or oxygen is important for decomposition because bacteria then take oxygen from the waste material itself and in the process break them down.
There are two types of bio gas plants that are used in India. These plants mainly use cattle dung called “gobar” and are hence called gobar gas plant. Generally slurry is made from cattle dung and water, which forms the starting material for these plants. The two types of bio gas plants are:
1. Floating gas holder type of plant:
A well is made out of concrete. This is called the digester tank. It is divided into two parts. One side has the inlet, from where slurry is fed to the tank. The tank has a cylindrical dome made of stainless steel that floats on the slurry and collects the gas generated.
Hence the name given to this type of plant is floating gas holder type of bio gas plant. The slurry is made to ferment for about 50 days. As more gas is made by the bacterial fermentation, the pressure inside cylindrical dome increases.
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The gas can be taken out through outlet pipe. The decomposed matter expands and overflows into the next chamber in tank. This is then removed by the outlet pipe to the overflow tank and is used as manure for cultivation purposes.
2. Fixed dome type of plant:
A well and a dome are made out of concrete. This is called the digester tank. The dome is fixed and hence the name given to this type of plant is fixed dome type of bio gas plant. The function of the plant is similar to the floating holder type bio gas plant. The used slurry expands and overflows into the overflow tank.
