Large quantities of sewage is generated everyday in cities and towns, which is treated in Sewage Treatment Plants (STPs) to make it less polluted. Given below is the flow diagram of one of the stages of STP.
Observe the given flow diagram and answer the questions accordingly

(a) Why primary effluent is passed into large aeration tanks?
(b) Write the technical term used for the sediment formed? Mention its significance
(c) Explain the final step that results in the formation of biogas in the large tank before the treated effluent is released into water bodies.

Explanation

(a) Vigorous growth of useful aerobic microbes into flocs.
(b) Activated sludge – some of it is pumped back into the aeration tank to serve as the inoculum
(c) During this digestion, a mixture of gases such as methane, hyrogensulphide is made and carbon dioxide. These gases form biogas.