Select the correct option regarding flocs.

In the sewage treatment process,the decomposer bacteria present in the waste are recycled at the beginning of the process. This is called.........

Three water samples namely river water,untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to $BOD$ test. The samples were labelled $A, B$ and $C$; but the laboratory attendant did not note which was which. The $BOD$ values of the three samples $A, B$ and $C$ were recorded as $20\, mg/L, 8\, mg/L$ and $400\, mg/L$ respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

What is sewage? In which way can sewage be harmful to us?

Given below is the flowchart of sewage treatment. Identify $A, B, C, D$ and $E$ and select the correct option.

Choose the correct sequence for $\text{STP}$ (Sewage treatment plant).