The above diagram shows a typical biogas plant. Explain the sequence of events occurring in a biogas plant. Identify a, b and c.

The biogas plant tank is fed with a mixture of dung or waste materials from kitchen and night soil along with water. The biogas tank is covered with a floating lid which keeps on rising as the gas is produced in the slurry due to the microbial activity of methanogens like Methanobacterium. Methanogens grow anaerobically on cellulosic material in cowdung to produce a large amount of methane, CO₂ and H₂. The biogas plant has an outlet, which is connected to a pipe to supply biogas. The leftover slurry is removed through another outlet and is used as fertiliser.

a: Sludge tank

b: Gas holder

c: Charge pit