Question

Water samples of BOD values of 4ppm and 18 ppm, respectively are:

A. highly polluted and clean
B. highly polluted and highly polluted
C. clean and highly polluted
D. clean and clean

Answer 1

Hint: To measure the amount of organic material or waste material present in the value BOD value is calculated. It checks how much of the oxygen will be required to break them biologically. BOD values for the clean water should be less or equal to 5 and for highly polluted it is more than 17ppm.

Complete step by step solution:
-BOD (Biological Oxygen Demand) is the measurement of how much amount of oxygen is consumed or taken by the microorganism and other bacteria to decompose the organic matter at specified temperature under aerobic condition. Aerobic condition happens in the presence of oxygen.
-Oxygen is the crucial component for all the natural water bodies but the amount of oxygen that is dissolved in water is very less. It is important because the presence of sufficient concentration of oxygen that is dissolved in water is important for maintaining aquatic life and to maintain the quality of lakes and streams.
-The organic matter in the water bodies affect the concentration of dissolved oxygen very badly. Some human induced factors and environmental factors tend to decrease the amount of dissolved oxygen in the water and due to this the stress on aquatic life increases.
-Biological oxygen demand is the amount of substances which are oxidizable in the water sample and hence lowers the dissolved oxygen concentration.
-BOD values are used to determine the condition of water and how much it is clean or polluted.
-BOD value for the clean water should be less than 5 or equal to 5 and the water which has a BOD value more than 17ppm are highly polluted.

Thus the correct option will be (C).

Note: With the increase in pollution in water BOD value will also increase. The water that we use in our daily life for drinking purposes should have a B0D value less than 5 ppm and if the BOD value will be more than 5ppm it will be harmful for us. In India the BOD value of the water must be less than 30ppm then only it can be disposed of in the water bodies and for treated water which is disposed in sewage plants have a BOD value of 100ppm.