Question

Biochemical Oxygen demand bod in river water

• A. Gives a measure of salmonella in the water
• B. Increases when sewage gets mixed with river water
• C. Remains unchanged when algal bloom occurs
• D. Has no relationship with the concentration of oxygen in the water.

Answer 1

The correct option is B

Increases when sewage gets mixed with river water

The correct option is B.

The explanation for the correct option:

1. Biochemical oxygen demand (BOD) is the number of oxygen microorganisms take to decompose organic waste matter in water.
2. It is therefore used as a measure of the number of certain types of organic pollutants in water.
3. Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one liter of polluted water.
4. If the water is polluted, more will be the BOD as more will be the organic matter present in it, and hence, more oxygen will be required to decompose it.
5. Hence, BOD in river water will increase if sewage gets mixed up with the river water because the organic matter will be added to the river.
6. Sewage is wastewater having food residue, animal and human excreta, detergent, and discharges from industrial and commercial establishments.
7. The degree of impurity of water due to organic matter is measured in terms of BOD or biochemical oxygen demand.
8. BOD is the oxygen in milligrams required for 5 days in one liter of water at 20 degrees centigrade for the microorganisms to metabolize organic wastes.
9. If the water, is polluted with sewage and other organic wastes, the BOD will increase.

The explanations of the incorrect options:

Option A:

1. The BOD does not give a measure of salmonella in the water.
2. This is an incorrect option.

Option C:

1. The value of BOD changes upon algal formation as the oxygen demand also changes due to the presence of algal blooms.
2. Hence, this is an incorrect option.

Option D:

1. This is an incorrect option as biological oxygen demand signifies the relationship between the availability of oxygen in the water body.

Final answer: Biochemical Oxygen demand BOD in river water increases when sewage gets mixed with river water.