What happens when domestic sewage mixes with river water?
Correct answer: C. The increased microbial activity uses up the dissolved oxygen.
- A. Small animals like rats will die after drinking river water.
- B. The increased microbial activity releases micronutrients such as iron.
- C. The increased microbial activity uses up the dissolved oxygen.
- D. The river water is still suitable for drinking as impurities are only about 0.1%.
Explanation
When sewage mixes with a water body, microorganisms present in it biodegrade the organic matter of the sewage using oxygen. This results in a sharp decline in dissolved oxygen which may cause mortality of aquatic creatures. Gradually, however, dissolved oxygen increases in concentration with the completion of biodegradation of sewage matter.
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