UPSC Prelims 2023 · GS Paper I
Question 55: Science and Technology
With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements :
- 1.Biofilters provide waste treatment by removing uneaten fish feed.
- 2.Biofilters convert ammonia present in fish waste to nitrate.
- 3.Biofilters increase phosphorus as nutrient for fish in water.
How many of the statements given above are correct?
AnswerUPSC’s answer is (b).
In a recirculating aquaculture system, biofilters host nitrifying bacteria that convert toxic ammonia from fish waste first to nitrite and then to nitrate, so statement 2 is correct. UPSC also counts statement 1 as correct, treating the biofilter as part of the waste-treatment loop that deals with breakdown products of uneaten feed. Statement 3 is wrong: biofilters do not add phosphorus for fish; they work on nitrogen wastes.
- 1. Per UPSC, biofilters contribute to waste treatment of feed breakdown products.
- 2. Nitrifying bacteria convert ammonia to nitrate.
- 3. Biofilters treat nitrogen wastes and do not supply phosphorus.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Only one undercounts the true statements.
- (b) Correct as per UPSC: statements 1 and 2 hold.
- (c) Statement 3 is wrong, so not all three.
- (d) Ammonia conversion is true, so not none.
Worth knowing: Strictly, uneaten feed and solids are removed by mechanical filtration and the biofilter treats dissolved waste, so statement 1 is loosely worded; this follows UPSC's key.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2023, General Studies Paper I, Series A. The paper on upsc.gov.in.