Question

Study the following statements and select the incorrect ones.
(i) Physical removal of large and small particles through filtration and sedimentation is called primary sewage treatment
(ii) Secondary sewage treatment is mainly a mechanical process
(iii) Activated sludge sediment in a sewage treatment plant is a rich source of aerobic bacteria
(iv) Biogas, commonly called as gobar gas, is pure methane

• A. (i) and (ii)
• B. (ii) and (iv)
• C. (ii) and (iii)
• D. (iii) and (iv)

Answer 1

The correct option is B (ii) and (iv)

Secondary treatment is also called biological treatment or microbial degradation. It is mainly a biological process.

Biogas is a mixture of gases, containing predominantly methane. It also contains $C{O}_2$ and traces of hydrogen $H_{2}S$, nitrogen, etc.