Q. 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?
- Only one
- Only two
- All three
- None.
Answer: (a) Only one
Biofilters
- Biofilters are a key component in the filtration portion of a recirculating aquaculture system (RAS).
- They house the nitrifying bacteria and are the primary site where biological nitrification occurs. The biofilters convert ammonia present in fish waste to nitrate.
- Ammonia is removed from an aquarium system through the use of a biofilter. The biofilter provides a substrate on which nitrifying bacteria grow. These nitrifying bacteria consume ammonia and produce nitrite, which is also toxic to fish. Other nitrifying bacteria in the biofilter consume nitrite and produce nitrate.
- For healthy and fast growth of aquatic species, fish feed needs to be supplied on a regular basis. This will in turn contaminate pond water due to presence of uneaten food material, fish fecal matter, growth of algae and other microorganisms. This contaminated water needs to be treated. These are removed at the level of tank and system treatment zones otherwise it would be detrimental to the efficiency of biofilters.
- Biofilters are used to reduce (not increase) the amount of phosphorus in water. Submerged flow biofilters, utilising a filter media were used to remove nitrogen and phosphorus from a synthetic fish farm water. The cyclic aerated/unaerated combined nutrients removal system achieved approximately 40 percent phosphorus removal, complete nitrification and 40 percent denitrification.