Environmental health: sewage treatment: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Environmental health: sewage treatment

Sample item

In the treatment of sewage, which stage uses aerobic micro-organisms in an aerated tank, as in the activated sludge process, to oxidise dissolved organic matter?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Secondary treatment

Secondary treatment is biological and aerobic, using activated sludge or trickling filters to oxidise organic matter and lower BOD. Preliminary treatment removes large and heavy solids, and primary treatment removes settleable solids by sedimentation. The settled sludge is stabilised separately in anaerobic digesters.

Option by option

  • A. Preliminary screening and grit removal

    Screening and grit removal are mechanical steps for coarse solids.

  • B. Primary treatment

    Primary treatment is physical sedimentation.

  • C. Anaerobic sludge digestion

    Sludge digestion is anaerobic and is applied to the settled sludge.

  • D. Secondary treatment (correct)

    Correct. Activated sludge is a secondary aerobic process.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, Secondary treatment. Secondary treatment is biological and aerobic, using activated sludge or trickling filters to oxidise organic matter and lower BOD.

Why is "Preliminary screening and grit removal" not the answer?

Screening and grit removal are mechanical steps for coarse solids.

Why is "Primary treatment" not the answer?

Primary treatment is physical sedimentation.

Why is "Anaerobic sludge digestion" not the answer?

Sludge digestion is anaerobic and is applied to the settled sludge.

What concept does this question test?

It tests Environmental health: sewage treatment in PSM. Preliminary treatment removes large and heavy solids, and primary treatment removes settleable solids by sedimentation. The settled sludge is stabilised separately in anaerobic digesters.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health: sewage treatment?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.