Environmental health: rapid sand filter cleaning: 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: rapid sand filter cleaning

Sample item

A town water works uses filters that depend on prior coagulation with alum and are cleaned by reversing the flow of water through the bed, instead of scraping the top layer. Which filter is this?

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

The answer and the reasoning

B. Rapid sand filter

Rapid sand filters follow coagulation, flocculation and sedimentation and run at high rates. They are cleaned by backwashing, which reverses the flow. Slow sand filters rely on a biological layer called the schmutzdecke and are cleaned by scraping the top few centimetres.

Option by option

  • A. Slow sand filter

    Slow sand filters are cleaned by scraping the surface layer and do not need coagulation.

  • B. Rapid sand filter (correct)

    Correct. Rapid sand filters use alum coagulation and are cleaned by backwashing.

  • C. Biological filter

    A biological filter is a method of sewage treatment and not for municipal water filtration.

  • D. Candle filter

    A candle filter is a household device with a ceramic element, not a municipal bed.

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 B, Rapid sand filter. Rapid sand filters follow coagulation, flocculation and sedimentation and run at high rates.

Why is "Slow sand filter" not the answer?

Slow sand filters are cleaned by scraping the surface layer and do not need coagulation.

Why is "Biological filter" not the answer?

A biological filter is a method of sewage treatment and not for municipal water filtration.

Why is "Candle filter" not the answer?

A candle filter is a household device with a ceramic element, not a municipal bed.

What concept does this question test?

It tests Environmental health: rapid sand filter cleaning in PSM. They are cleaned by backwashing, which reverses the flow. Slow sand filters rely on a biological layer called the schmutzdecke and are cleaned by scraping the top few centimetres.

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: rapid sand filter cleaning?

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.