Question

High value of BOD (Biochemical Oxygen Demand) indicates
A. Water is less polluted
B. Consumption of organic matter in the water is higher by the microbes
C. Water is pure
D. None of these

Answer 1

Biochemical oxygen demand is the amount of oxygen consumed by microorganisms during decomposition, higher the value of organic waste present in the water higher the value of BOD required by the microorganism.

Complete answer:
The biochemical oxygen demand represents the amount of oxygen consumed by microorganisms like bacteria while they are decomposing the organic matter under aerobic conditions at a specific temperature. In other words, Biochemical oxygen demand can be defined as the amount of dissolved oxygen that is needed or demanded by the aerobic biological organisms present in the water to break down the organic material present, at a certain temperature over a specified period of time. It is the surrogate of the degree of organic pollution of water.
-The Biochemical oxygen demand value or the BOD value is usually expressed in milligrams of oxygen consumed per liter of the sample during 5 days of incubation at 20°C.
-If the value of the Biochemical oxygen demand of any water sample will be high, then it will indicate that a large amount of oxygen has been consumed to decompose the organic matter by the microorganisms. For large amounts of decomposition, a large number of bacterias as well as a large number of organic waste will be needed.
-Water pollution is defined as the contamination of water with unwanted substances. Hence, a large amount of organic wastes in water indicates a high rate of water pollution.
-Thus based on the above information, the high value of BOD (Biochemical Oxygen Demand) indicates that the consumption of organic matter in the water is higher by the microbes
Hence option B is correct.

Note: Biochemical oxygen demand is more like the indicator of bacterias present in water than pollution though it is used for the latter as we do not have other better ways. But it is not the correct indicator as the presence of organic substances can necessarily be not termed as water pollution only.