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Q55 (IAS/2023) Science & Technology › New Materials, Energy & Environment-linked Tech › Water and sanitation technologies Official Key

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?

Result
Your answer: —  ·  Correct: B
Explanation

The correct answer is Option 2 (Only two). This is because statements 1 and 2 are scientifically accurate regarding the function of biofilters in a Recirculating Aquaculture System (RAS), while statement 3 is incorrect.

  • Statement 1 is correct: Biofilters play a crucial role in waste treatment. While mechanical filters remove large suspended solids, biofilters house microbial communities that break down organic wastes, including dissolved organic compounds from uneaten fish feed.
  • Statement 2 is correct: This is the primary function of a biofilter. Through the process of nitrification, specialized bacteria (like Nitrosomonas and Nitrobacter) convert toxic ammonia, excreted by fish, into nitrite and then into relatively harmless nitrate.
  • Statement 3 is incorrect: Biofilters do not aim to increase phosphorus. In fact, excessive phosphorus can lead to algae blooms and water quality degradation; RAS designs typically focus on removing or managing phosphorus rather than increasing it as a nutrient.
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements : 1. Biofilters provide …
At a glance
Origin: Books + Current Affairs Fairness: Low / Borderline fairness Books / CA: 3.3/10 · 6.7/10
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This is a 'Technology in Agriculture' question masquerading as Environment. While Statement 2 is basic static ecology (Nitrogen Cycle), Statements 1 and 3 require understanding the engineering process flow of RAS. Strategy: When a tech like RAS/Biofloc is in the news, don't just read the benefits; look up the 'schematic diagram' to see which component does what.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Do biofilters in recirculating aquaculture systems remove uneaten fish feed (solid particulate waste)?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"This strategy requires the effluent water to be fully filtered to remove particulate waste, stripped of gases such as carbon dioxide and nitrified to remove toxic levels of"
Why this source?
  • Explicitly states particulate waste is removed by filtration (separately) before nitrification.
  • Implies particulate removal is a different step from biofiltration (which handles nitrification).
Web source
Presence: 4/5
"Biological filters are essential parts of recirculating aquaculture systems that transform toxic fish compounds such as ammonium and nitrite into less-harmful nitrate."
Why this source?
  • Defines the role of biological (bio)filters as transforming dissolved toxic compounds (ammonium, nitrite) to nitrate.
  • By specifying dissolved-N transformation, it implies biofilters treat dissolved waste, not solid particulates like uneaten feed.
Web source
Presence: 4/5
"Evaluation of the nitrification rates of microbead and trickling filters in an intensive recirculating tilapia production facility."
Why this source?
  • Refers to evaluation of nitrification rates of microbead and trickling filters, indicating these biofilters are for nitrification (dissolved nitrogen removal).
  • Supports distinction between biofilters (nitrifying) and mechanical/physical filters for particulates.

Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > 2. Fish Farming > p. 90
Strength: 4/5
“Fish farming is the principal form of aquaculture, while other methods may fall under mariculture. It involves raising fish commercially in tanks or enclosures, usually for food. Fish species raised by fish farms include salmon, catfish, tilapia, cod, carp, trout, and others. Increasing demands on wild fisheries by commercial fishing operations have caused widespread overfishing. Fish farming offers an alternative solution to the increasing market demand for fish and fish protein.”
Why relevant

Defines fish farming as raising fish in tanks/enclosures where feeding occurs — implying production of feed-related wastes in such systems.

How to extend

A student could combine this with knowledge of tank systems to ask which components (mechanical vs biological) handle different waste types.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 6. Commercial Fishing & Aquaculture > p. 47
Strength: 4/5
“• Over exploitation of target fish stock due to increased demand (e.g., all the Indian estuaries) • Reclaiming the fringed areas for intensive aquaculture in pens, • · obstructing the migratory routes of fish and prawn recruitment (e.g., Chilika, Pulicat) • Polluting the environment through feeding of stocked fish and prawn in pens (Chilika) • Destruction of biodiversity through prawn seed collection and operation of small-meshed nets (e.g., Hooghly, Chilika, Pulicat)”
Why relevant

States that feeding of stocked fish can pollute the environment, linking fish feed to waste and water-quality problems.

How to extend

One could infer that aquaculture systems need waste-management components and then check whether biofilters address particulate versus dissolved wastes.

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 6: Environmental Degradation and Management > Solid Waste > p. 44
Strength: 4/5
“Te solid waste may be safely disposed of in the following ways: (i) open dumps, (ii) landflls, (iii) sanitary land flls, (iv) Incineration plants, (v) composting, (vi) vermiculture or earthworms farming, (vii) bioremediation or the use of micro-organisms (bacteria and fungi) to degrade the environmental contaminants into less toxic forms, and (viii) pyrolysis – a process of combustion in the absence of oxygen.”
Why relevant

Lists bioremediation (use of microbes) as a method to degrade environmental contaminants and solid waste.

How to extend

Since biofilters rely on microbial processes, a student could explore whether microbial treatment targets dissolved compounds or also degrades solid particulates like uneaten feed.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.3 Rearoval of the nutrients from a lake > p. 38
Strength: 5/5
“• Rushing with nutrient-poor waters. • R Deep water abstraction. • On-site P-elimination by flocculation/flotation with water backflow, or floating Plant NESSIE with adsorbents. • On-site algae removal by filters and P-adsorbers. • On-site algae skimming and separator thickening. • Artificial mixing / Destratification (permanent or intermittent). • Introduction of fishes and macrophytes. • Sludge removal.”
Why relevant

Gives a list of on-site nutrient and algae removal techniques including filters and sludge removal, distinguishing mechanical removal (filters/sludge) from other treatments.

How to extend

A student could use this to hypothesize that physical filters/sludge removal handle solids, and then investigate whether 'biofilters' are listed among physical or biological treatments.

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Water Pollution > p. 33
Strength: 3/5
“Te aquatic ecosystems are facing serious threats both in the developing and the developed countries. Te main threat to aquatic ecosystems are from water-pollution, resulting mainly from sewage, disposal, dumping of garbage, and poorly managed solid and liquid waste. Te sewage disposal in aquatic ecosystems results into eutrophication. Eutrophication is the excessive growth of algae and other related organisms in a water-body as a result of the input of large amounts of nutrient ions, especially phosphate and nitrate. Te eutrophication destroys life in water, as oxygen content is severely reduced. Fish and crustaceans cannot breathe and get killed. Moreover, a foul odour is produced which destroy the fora and the fauna of the aquatic ecosystems.”
Why relevant

Explains eutrophication from inputs of nutrient-rich wastes (sewage, solid/liquid waste), linking organic/solid inputs to problems caused by dissolved nutrient release.

How to extend

A student could reason that uneaten feed may produce dissolved nutrients (causing eutrophication) after breakdown, and then ask whether biofilters remove the dissolved products or the original particulates.

Statement analysis

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Statement analysis

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