Question

Three water samples namely river water, untreated sewage water and secondary- effluent discharged from a sewage treatment 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 BOP values of the three samples A, B and C were recorded as 20mg/I... Smg/L and 400mg/L, respectively, Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water Is relatively clean?

Answer 1

BOD of untreated sewage water is 400mg/l because BOD of sewage water lies between 200 to 700 mg/l. So, sample C is untreated sewage water.

BOD of effluent discharged from a sewage treatment plant will be 20 mg/l because it should be less than 50 mg/l. So, sample A is effluent discharged from a sewage treatment plant .

So, sample B is river water.

Hope this may help you....!!