Question

Describe the construction and working of a biogas plant with the help of a labelled diagram.

Answer 1

 

Construction of a biogas plant
A biogas has an underground tank shaped like a well. It is called a digester and is made of bricks and cement. The dome of the digester acts as a storage facility for biogas. On the top of the dome, there is a gas outlet 'S' with a valve 'V'. A sloping inlet chamber 'I' is situated on the left side, and on the right side, there is a rectangular outlet chamber 'O'. The function of the inlet chamber is to introduce fresh dung slurry into the digester tank and that of the outlet chamber is to facilitate the removal of the spent slurry after the extraction of biogas.
Working
A slurry is made in the mixing tank by mixing cow dung and water and then fed into the digester tank through 'I'. The digester is filled up to the cylindrical level, the dome being left free for the collection of biogas. In 50-60 days, the cow dung undergoes degradation by anaerobic bacteria in the presence of water but in the absence of oxygen, with the gradual evolution of gas. The biogas that is formed gets collected in the dome and exerts pressure on the slurry in the tank for its removal through the outlet chamber.