Large quantities of sewage is generated every day 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.

Identify the correct set of gases produced during digestion of sludge:

Options

A. methane, hydrogen sulphide and carbon dioxide
B. methane, sulphur and carbon dioxide
C. carbon monooxide, methane, hydrogen sulphide
D. methane, hydrogen sulphide and nitrogen

Answer

A

Explanation

During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide, and carbon dioxide. These gases form biogas and can be used as a source of energy. The treated effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.