Zoology - Microbes in Human Welfare Question with Solution | TestHub

Sewage mixed with bacteria and fungi that thrive and multiply in it and lead to its oxidation. Activation reduces the organic pollution that raw sewage otherwise will impose on the body of water to which it is discharged.

Once the BOD of sewage or waste water is reduced significantly, the effluent is passed into a setting tank where the bacterial flocs undergo sedimentation and the sediment is thus called activated sludge.