BOD Levels and Water Pollution Assessment — NEET Biology
📚 Practice ConceptThree 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 BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/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?
Which of the above statements are correct? S1: The Biochemical Oxygen Demand (BOD) is directly proportional to the amount of inorganic pollutants present in a water sample. S2: Water with a BOD value of 400 mg/L is indicative of highly polluted raw sewage. S3: After secondary treatment, the effluent typically shows a BOD value similar to that of untreated sewage, making it suitable for discharge. S4: The BOD test measures the rate of oxygen uptake by microorganisms, thereby indirectly indicating the quantity of organic matter present. S5: Clean river water is characterized by a very high BOD, as it supports a diverse range of aquatic microorganisms.
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