Question

Explain the effect on the characteristics of a river when urban sewage is discharged into it. [3]

Answer 1

When urban sewage is discharged in a river [3]
1. There is a rise in organic matter.
2. There is increased microbial activity due to increased organic matter.
3. Dissolved oxygen concentration reduces.
4. There is a rise in BOD which leads to fish mortality, algae bloom, colour change, foul odour and increase in toxicity.