Question

The graph given below represents the effect of sewage discharge on some important characteristics of river.
Select the correct option with respect to the peaks A and B.

• A. Peak A- Sharp increase in BOD, disappearance of clean water organisms,Peak B- Increase in dissolved oxygen, reappearance of clean water organisms
• B. Peak A- Increase in dissolved oxygen, reappearance of clean water organisms,Peak B- Sharp decline in dissolved oxygen, disappearance of clean water organisms
• C. Peak A- Sharp increase in BOD, appearance of clean water organisms,Peak B- Increased in dissolved oxygen, disappearance of clean water organisms
• D. Peak A- Increased number of anaerobic bacteria, disappearance of clean water organisms,Peak B- sharp decline in dissolved $O_2$, reappearance of clean water organisms

Answer 1

Answer: (A)

Peak A- Sharp increase in BOD, disappearance of clean water organisms,Peak B- Increase in dissolved oxygen, reappearance of clean water organisms

Rich growth of the microorganism in the lakes consumes most of the dissolved oxygen. This condition is known as Eutrophication.

The excessive plant nutrients intensify eutrophication.

The impurity of water due to organic matter is measured in terms of biological oxygen demand. It is the demand for oxygen to decompose organic waste in litre of water. So where the BOD is high means the water is polluted and the organic matter is high. It shows that the sewage increase in biochemical oxygen demands of water as it has a lot of organic material.

So, the correct option is 'Peak A- Sharp increase in BOD, the disappearance of clean water organisms, Peak B- Increase in dissolved oxygen, the reappearance of clean water organisms'