Explain the principle and working of a biogas plant using a labelled schematic diagram.


Biogas is produced as a result of anaerobic fermentation of biomass in the presence of water.

Construction Back to Top

The biogas plant is a brick and cement structure having the following five sections:

  • Mixing tank present above the ground level.
  • Inlet chamber: The mixing tank opens underground into a sloping inlet chamber.
  • 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.
  • Outlet chamber: The digester opens from below into an outlet chamber.
  • Overflow tank: The outlet chamber opens from the top into a small over flow tank.

Fixed Dome type Biogas Plant

Working Back to Top
  • The various forms of biomass are mixed with an equal quantity of water in the mixing tank. This forms the slurry.
  • The slurry is fed into the digester through the inlet chamber.
  • When the digester is partially filled with the slurry, the introduction of slurry is stopped and the plant is left unused for about two months.
  • During these two months, anaerobic bacteria present in the slurry decomposes or ferments the biomass in the presence of water.
  • As a result of anaerobic fermentation, biogas is formed, which starts collecting in the dome of the digester.
  • As more and more biogas starts collecting, the pressure exerted by the biogas forces the spent slurry into the outlet chamber.
  • From the outlet chamber, the spent slurry overflows into the overflow tank.
  • The spent slurry is manually removed from the overflow tank and used as manure for plants.
  • The gas valve connected to a system of pipelines is opened when a supply of biogas is required.
  • To obtain a continuous supply of biogas, a functioning plant can be fed continuously with the prepared slurry.

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