In how many stages does sewage treatment occur?

Select the appropriate option regarding the aeration tank.

Assertion $(A)$: There is a need for more sewage treatment plants in proportion to the human population.
Reason $(R)$: Biogas is produced as fuel energy in $STPs$.
Which option is correct for Assertion $(A)$ and Reason $(R)$?

The high amount of $E. coli$ in water is the indicator of

What is the water obtained after the sedimentation process in sewage treatment called?

Select the mismatched option from the following.