Question

what are the uses of the activated sludge​

Answer 1

The sludge (semi solid material, by product of waste water treatment) contains high concentration of living or active microorganism.

And by returning a portion of this activated sludge to the reactor, there will be increase in biomass(microorganisms) and speed up the digestion of organic matters present in reactor.

Thus reduces the detention time.

Answer 2

Explanation:

The residue that accumulates in sewage treatment plants is called sludge (or biosolids). Digested sludge is passed through a dewatering step; the dried solids are disposed of, and the water is sent back to secondary treatment. ...