Question

Limit of B.O.D. prescribed by Central Pollution Control Board for the discharge of industrial and municipal waste waters into natural surface waters is
A. \[ < 30ppm\]
B. \[ < 3.0ppm\]
C. \[ < 10ppm\]
D. \[ < 100ppm\]

Answer 1

Hint: Biological oxygen demand (or B.O.D.) is referred as the total oxygen amount required by the microorganisms that are normally present in a water body to break down the organic constituents of water. Higher the B.O.D., more abundant will be the microorganism in the water body, and greater will be the pollution due to organic matter.

Complete answer:
BOD increases with increased number of microorganisms in a water body as the microorganisms would require oxygen for their metabolic activities during the process of breaking down the organic waste present in it. The water is considered good if its BOD level is \[1 - 2ppm\]. However, the water is considered to be slightly polluted in case its BOD level is about \[3 - 9ppm\]. CPCB (Central Pollution Control Board) has prescribed the BOD limit for safe discharge of the municipal and industrial waste into the surface water bodies present in nature. This helps ensure the proper regulation of water pollution, and efficient treatment of the water. Hence, the BOD limit prescribed by CPCB for the discharge of industrial and municipal waste waters into natural surface waters is considered to be less than \[10ppm\]. This is because any factor contributing to an increased BOD would make the water polluted, and the water with BOD more than \[10ppm\] is generally considered greatly polluted.

The correct answer is option C, stating \[ < 10ppm\].

Note:
B.O.D is often determined in parts per million (ppm). The industrial wastes, insecticides, herbicides, sewages and other pollutants greatly influence the BOD in a water body. As a result, the water gets more polluted depending upon the amount of wastes dumped into it.