Which microorganisms are used for the purification of sewage water?

$(a)$ 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?

The microorganisms involved in floc formation during sewage treatment are

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

Sewage water can be purified for recycling with the action of

Assertion $(S)$: Flocs are organisms that consume inorganic substances in water.
Reason $(R)$: $STPs$ are used to prevent water pollution.