Question

BOD level in freshwater should not exceed beyond
(a) 5 ppm
(b) 10 ppm
(c) 25 ppm
(d) 50 ppm

Answer 1

Hint: Higher the value of BOD higher will be the pollutant level in the water. This is a unit that is used to know about the amount of organic pollutants in the given water body.

Complete answer:
BOD ( Biochemical Oxygen Demand) level in freshwater should not exceed 50 ppm.
BOD is the amount of oxygen required to decompose or for the breakdown of organic matter present in one liter of polluted water. It informs us about the number of organic pollutants present in the water sample. The more value of BOD will indicate the increased amount of organic matter in the water. Hence, a high value of BOD shows that the water is heavily polluted. The advised level of BOD in freshwater is 50 parts per million. This means that for per million freshwater 50 parts of organic matter is considerable, or we can say that in a one- liter sample of polluted water presence of 50 parts of the organic matter is advisable.
Water with a BOD value of 1- 2 ppm is considered pure and clean.
In freshwater, BOD value should not exceed 5 ppm because the dissolved oxygen will get used up in the decomposition of organic matter and will not remain available for the survival of aquatic organisms which will cause the death of aquatic organisms. It is also used for determining the amount of dissolved oxygen required for aerobic biological organisms in a body of water to break down or disintegrate organic material present in a given water sample at a certain temperature over a specific period.
So, the correct answer is, '50 ppm'.

Note:
- Ppm means parts per million.
- Different countries prescribe different discharge limits. Malaysia, for example, has a BOD limit of 20 and 50 mg/l.
- The treated effluent quality limit & safe disposal is standardized by the Environmental Protection Agency (EPA) .