Q. 21 Why do we prefer to call secondary waste water treatment as biological treatment?

Secondary waste water treatment is called biological treatment because microorganisms

are involved in the breakdown of organic matter in this phase of waste water treatment.

The primary effiuent is passed into large aeration tanks where the organic matter in it is

consumed by aerobic microbes which are later themselves digested by anaerobic bacteria

and fungi in anaerobic sludge digesters.