Select the appropriate option regarding secondary treatment.

$(a)$ What would happen if a large volume of untreated sewage is discharged into a river?
$(b)$ In what way is anaerobic sludge digestion important in sewage treatment?

$A$: More sewage treatment plants are required in proportion to the human population.
$R$: Biogas,which is a fuel energy,is produced in $STPs$.

What would happen if oxygen availability to activated sludge flocs is reduced?

In a sewage treatment plant,primary treatment is

In which tanks do the formation of flocs and the sedimentation of flocs occur,respectively?