Question

water filled in two gasses A and B have BOD values of $10$ and $20$ , respectively.
The correct statement regarding them, is :
A. A is more polluted than B
B. A is suitable for drinking , whereas B is not
C. B is more polluted than A
D. Both A and B are suitable for drinking.

Answer 1

The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during $5$ days of incubation at $20{\text{ }}^\circ C$ and is often used as a surrogate of the degree of organic pollution of water The test for biochemical oxygen demand (BOD) is a bioassay procedure that measures the oxygen consumed by bacteria from the decomposition of organic matter (Sawyer and McCarty, $1978$).

Complete step by step answer:
Two glasses "A" and "B" have BOD values 10 and "20", respectively. Hence glasses "B" is more polluted than glasses "A". A BOD level of $1 - 2$ppm is considered very good. There will not be much organic waste present in the water supply. A water supply with a BOD level of $3 - 5$ ppm is considered moderately clean. The test for biochemical oxygen demand (BOD) is a bioassay procedure that measures the oxygen consumed by bacteria from the decomposition of organic matter (Sawyer and McCarty, $1978$) . Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on, and signifies lower water quality. Inversely, low BOD means less oxygen is being removed from water, so water is generally purer.

Hence correct option is (C)

Note: BOD reduction is used as a gauge of the effectiveness of wastewater treatment plants. Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on, and signifies lower water quality.