Question

Read the following statements (A-D) related to Biochemical Oxygen Demand (BOD) and identify the correct option stating true (T) and false (F).

A. Biochemical oxygen demand is defined as the amount of dissolved oxygen needed by microorganisms in decomposing the inorganic wastes.
B. Greater the BOD of waste water, the higher is the amount of organic matter present.
C. The BOD increases with time as organic matter gets decomposed.
D. Sewage water is treated till the BOD is reduced

• A. A - F, B - T, C - F, D - T
• B. A - F, B - F, C - F, D - T
• C. A - T, B - T, C - F, D - T
• D. A - F, B - T, C - F, D - F

Answer 1

The correct option is A A - F, B - T, C - F, D - T

Biochemical Oxygen Demand (BOD) is the amount of oxygen consumed by the aerobic bacteria for the oxidation of all the organic matter present in one litre of water.

Hence, statement A is false.

When untreated domestic sewage is discharged into water bodies, it raises the BOD, as the decomposers consume lots of oxygen to degrade the organic matter (OM). Organic matter includes leaves, woody debris, dead plants and animals, animal manure, effluents from pulp and paper mills, food-processing plants etc. Therefore, BOD is high for water with high organic matter as the bacteria breakdown the organic matter in the wastewater and this metabolic process sharply increases the oxygen consumption.

Hence, statement B is true.

Eventually with time, the BOD decreases as the organic matter is decomposed.

Hence, statement C is false.

The greater the BOD of sewage water, more is its polluting potential. So, the sewage water is treated, till its BOD is reduced to reduce the organic matter present in it.

Hence, statement D is true.


Figure: Biochemical Oxygen Demand (BOD)