Question

Biochemical oxygen demand in a river water

• A. Remains unchanged when algal bloom occurs
• B. Increases when sewage gets mixed up with river water
• C. Has no relationship with concentration of oxygen in water
• D. Gives a measure of Salmonella in water

Answer 1

Answer: (B)

Increases when sewage gets mixed up with river water

Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one litre of polluted water.

If the water is more polluted, more will be the BOD because more will be the organic matter present in it and hence, more oxygen will be required to decompose it.

Hence, BOD in a river water will increase if sewage gets mixed up with the river water because more organic matter will be added in the river.

So, the correct answer is 'Increases when sewage gets mixed up with river water'.