Question

Clean water would have Biochemical Oxygen Demand (BOD) value of less than:
(A) 17 ppm
(B) 5 ppm
(C) 200,00 ppm
(D) 10 ppm

Answer 1

Hint: The BOD value is the measure of the amount of organic material present in water, in terms of how much oxygen would be required to break it down biologically. Oxygen demand is the number of substances that are oxidizable in a water sample which can lower the dissolved oxygen concentrations.

Complete answer: 
* Biochemical Oxygen Demand is the measure of the amount of oxygen that is consumed by the bacteria and other microorganisms while they decompose, under the aerobic conditions (presence of oxygen), the organic matter at specified temperatures. Although the amount of oxygen that is dissolved in the water is very small, it is a crucial component of all the natural water bodies. It is because the presence of sufficient concentrations of dissolved oxygen is critical to maintaining the aquatic life and also the quality of streams and lakes.

The determination of how the organic matter affects the concentration of the dissolved 
* Oxygen is very integral to water - quality management.
* There are certain environmental stresses and human-induced factors that tend to lessen the amount of dissolved oxygen thereby resulting in stresses on aquatic life.
* The BOD value describes how clean the water is or the amount of pollution present in it.
The BOD value of 
* Moderately clean water is 3-5 ppm, whereas somewhat polluted water has a BOD value of 6-9 ppm.
* The BOD value of clean water would be less than or equal to 5 ppm.

Therefore, the correct answer is option (b).

Note: The BOD value increases as the amount of pollution increases in a water body. The water that we drink should have a BOD value of less than 5 ppm. The wastewater that is disposed off in the water bodies in India should have a BOD level of less than 30 ppm and the treated water that is discharged into the sewerage system has a BOD level of 100 ppm.