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NEET-UG Biology

Microbes in sewage treatment — practice questions

7 questions in the bank on this idea. Below are 7 of them, exactly as they appear in a test.

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  1. Question 1 · difficulty L1 · recall

    What does BOD measure in sewage treatment?

    • A. The total amount of dissolved salt
    • B. Oxygen used during microbial decomposition
    • C. The number of viruses only
    • D. Methane concentration in treated drinking water after complete purification

  2. Question 2 · difficulty L2 · understanding

    What is the main purpose of primary sewage treatment?

    • A. Methane production only
    • B. Complete biological oxidation of dissolved organics
    • C. Physical removal of large and suspended particles
    • D. Sterilisation of all water

  3. Question 3 · difficulty L2 · understanding

    What are flocs in secondary sewage treatment?

    • A. Methane bubbles coated with suspended oil and mineral particles
    • B. Large mineral crystals
    • C. Clusters of red blood cells
    • D. Bacterial-fungal microbial aggregates

  4. Question 4 · difficulty L3 · understanding

    Which of the following is put into Anaerobic sludge digester for further sewage treatment?

    • A. Effluents of primary treatment
    • B. Primary sludge
    • C. Floating debris
    • D. Activated sludge

  5. Question 5 · difficulty L3 · application

    Why is air pumped into aeration tanks during secondary sewage treatment?

    • A. To supply oxygen to aerobic decomposers
    • B. To encourage obligate anaerobic methanogens to multiply aerobically
    • C. To precipitate every dissolved salt
    • D. To stop microbial respiration

  6. Question 6 · difficulty L4 · analysis

    After secondary treatment, part of the activated sludge is returned to the aeration tank. Why?

    • A. To increase the amount of untreated organic waste entering the tank
    • B. To seed the tank with active microbes
    • C. To eliminate oxygen from the tank
    • D. To stop floc formation

  7. Question 7 · difficulty L5 · analysis

    Untreated sewage entering a river causes a sharp rise in BOD. What ecological effect is most likely downstream?

    • A. Organic matter disappears rapidly without any microbial respiration
    • B. Dissolved oxygen necessarily rises
    • C. Dissolved oxygen falls
    • D. Aquatic respiration stops using oxygen

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