Which of the following parameters are used to categorize the river stretches as critically polluted, severely polluted, moderately polluted, less polluted or good? (i). Biological Oxygen Demand (ii). Fecal Coliform (iii). Chemical Oxygen Demand (iv). Turbidity
- A(i) and (ii)Correct
- B(i) and (iii)
- C(i), (ii) and (iii)
- D(i), (ii), (iii) and (iv)
Solution
Concept
CPCB classifies polluted river stretches using BOD (and, in newer criteria, fecal coliform).
Step-by-step solution
1. CPCB identified polluted river stretches by priority classes (I to V). 2. The classes were based on BOD levels. 3. Fecal coliform has been added in newer criteria along with BOD. 4. COD and turbidity are not used for this categorisation. 5. So the answer is (i) and (ii), option A.
Explanation
River stretches are graded as critically, severely or moderately polluted mainly by BOD, with fecal coliform used along with it in the newer criteria. COD and turbidity are not used for these grades.
Why the other options are wrong
B, C and D include COD and/or turbidity, which are not used for this grading.
Shortcut
River pollution grade = BOD + fecal coliform.
Common mistake
Adding COD because it is also a pollution measure.
Correct answer: A) (i) and (ii)