Question

The fishes were present in the river, but algaes were not able to survive. What is the zone of pollution of the river?

(a) Zone of recovery

(b) Zone of degradation

(c) Zone of clean water

(d) Zone of active decomposition

This question was posed to me during an online interview.

The above asked question is from Pollution Zones in River topic in chapter Natural Methods of Wastewater Disposal of Environmental Engineering

Answer 1

The correct choice is (b) Zone of degradation

To explain I would say: It is the zone of degradation as dissolved oxygen has reduced to 40%. The fishes will die when dissolved oxygen is less than 4ppm.