Question

Biochemical Oxygen Demand (BOD) in a river water

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

Answer 1

The correct option is D Increases when sewage gets mixed with river water.

Sewage is waste water having food residue, animal and human excreta, detergent, discharges from industrial and commercial establishments. Degree of impurity of water due to organic matter is measured in terms of BOD or biochemical oxygen demand. BOD is the oxygen in milligrams required for 5 days in one litre of water at 20 degree centigrade for the micro organisms to metabolise organic wastes. If the water, is polluted with sewage and other organic wastes, the BOD will increase.