Disposal of Sewage Effluents MCQ with answer and solution

Concept

Biochemical Oxygen Demand (BOD) and Dissolved Oxygen Depletion

Formula

N/A

Step-by-step solution

1. Understand the cause of dissolved oxygen depletion when sewage enters a flowing river. 2. Recall that microorganisms consume dissolved oxygen during the decomposition of organic waste. 3. Select Option D as the correct choice.

Explanation

When sewage is discharged into a river, it brings in a large amount of organic waste. Microorganisms (like aerobic bacteria) rapidly feed on and decompose this organic matter. During this breakdown process, these microbes consume significant amounts of oxygen dissolved in the water, leading to its rapid depletion.

Shortcut

To remember why dissolved oxygen drops when sewage enters a river, use the phrase "Microbes Eat Waste, Drain Oxygen": - Microbes Eat Waste: Aerobic bacteria rapidly decompose organic matter in sewage. - Drain Oxygen: As microbes feed and break down the waste, they consume and rapidly deplete the river's dissolved oxygen.

Common mistake

A common mistake is selecting option C by assuming that aquatic plants cause the rapid drop in dissolved oxygen, whereas the primary cause is aerobic microorganisms consuming oxygen while breaking down organic matter. Another frequent error is selecting option B, confusing physical suspended solids with the biological process of oxygen consumption.