Given below is the flow chart of sewage treatment. Identify $\mathrm{A},\mathrm{ }\mathrm{B},\mathrm{ }\mathrm{C}$ and $\mathrm{D}$ and select the correct option.

 

Read the following statements and select the incorrect one.

Match Column I with Column II and select the correct answer from the given codes.

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 gobar gas is pure methane.

Which of the following bacteria is present in the rumen of cattle?

Process of biogas production is