In $B.O.D.$ test,oxygen plays an important role to

$BOD$ refers to

Which organisms grow when air is passed through primary effluent using mechanical agitation?

Select the mismatched option from the following:

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 $(R)$?

Which process is used to remove floating debris from sewage?