Question

Sewage water is purified for reuse by the action of

• A. Protozoans
• B. Micro-organisms
• C. Plants and light
• D. Fish

Answer 1

The correct option is B Micro-organisms

Domestic sewage consists biodegradable organic matter and easily decomposes by the micro-organisms. These microorganisms can multiply using these organic substances as substrates and hence, utilize some of the components of sewage. Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result, there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic creatures.

Thus, the correct answer is option B.