Question

In which pollution zone of the river, the concentration of D.O reduced to 40%?

(a) Zone of degradation

(b) Zone of recovery

(c) Zone of active decomposition

(d) Zone of clean water

I have been asked this question in an international level competition.

This interesting question is from Pollution Zones in River topic in section Natural Methods of Wastewater Disposal of Environmental Engineering

Answer 1

Right choice is (c) Zone of active decomposition

Explanation: In the zone of active decomposition, the concentration of D.O reduced to 40%. It is the second zone of pollution in the river.