With reference to the role of biofilters in Recirculating Aquaculture System, consider the following

Q: What is UPSC Prelims?

UPSC Prelims is a competitive examination conducted in India. This question is from the 2023 UPSC Prelims Environment & Ecology paper.

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This UPSC Prelims 2023 Environment & Ecology question has a medium difficulty level and is marked as an important question.

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Question

With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements:Biofilters provide waste treatment by removing uneaten fish feed.Biofilters convert ammonia present in fish waste to nitrate.Biofilters increase phosphorus as nutrient for fish in water.How many of the statements given above are correct?

Accepted Answer

Correct Answer: B — Only twoStep-by-step Solution:A Recirculating Aquaculture System (RAS) is an indoor, tank-based fish farming system where water is continuously treated and recirculated rather than discarded. Biofilters are a critical component of RAS water treatment.Statement 1 — Biofilters remove uneaten fish feed: This is correct. Biofilters use microorganisms fixed to a substrate (inorganic or organic medium) to break down various pollutants in the water, including uneaten feed and organic waste from fish excretion. The biological and physical components of biofilters help purify the water and remove harmful waste products. ✓Statement 2 — Biofilters convert ammonia to nitrate: This is correct. This is the primary biochemical function of biofilters — the nitrification process: (a) Ammonia (from fish waste and decomposing feed) is first converted to nitrite by Nitrosomonas bacteria; (b) Nitrite is then converted to nitrate by Nitrobacter bacteria. Nitrate is far less toxic to fish than ammonia or nitrite, so this two-step conversion is essential for fish health in a recirculating system. ✓Statement 3 — Biofilters increase phosphorus as nutrient for fish: This is incorrect. Biofilters do NOT increase phosphorus in the water — they actually help remove phosphorus waste by-products generated by fish. In RAS, phosphorus accumulates as a waste product and must be managed; biofilters help control phosphorus levels rather than augmenting them. ✗Why other options are incorrect:Option A (Only one): Incorrect — two statements (1 and 2) are correct.Option C (All three): Incorrect — statement 3 is false.Option D (None): Incorrect — statements 1 and 2 are correct.Key Concept: Biofilters in RAS work through biological nitrification — a two-step aerobic process essential for water quality management. They are also used in industrial wastewater treatment and for controlling odorous gases. RAS technology is gaining importance in India for sustainable aquaculture, especially for high-value fish species, as it minimises water usage and environmental pollution.

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