Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatement plant were subjected to BOD test. The samples were labelled A, B and C. but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/L and 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct to each assuming the river water is relatively clean ?

Explanation

If the BOD level of A,B and C are 20 mg/L, 8 mg/L and 400 mg/L, the most polluted one is sample .C. i.e., untreated sewage water. Sample B is the least polluted and it is river water. Sample A is secondary effluent discharged from a treatement plant.