This unit of measure is usually referred to as the specific surface area (SSA) of the biofilter media. To make biofilters more compact, material that has a large surface area per unit volume is usually chosen. A biological filter consists of non-corroding material such as plastic, fiberglass, ceramic or rock that has large amounts of surface area nitrifying bacteria cells can colonise. Starting a biofilter involves managing and controlling the seeding of nitrifying bacteria cells in a biological filter. The reaction sequence accomplished by the nitrifying bacteria can be simplified as follows: 451, Recirculating Aquaculture Tank Production Systems: An Overview of Critical Considerations. Further information can be found in SRAC Publication No. Nitrate is the end product of the conversion of ammonia and nitrite and is non-toxic at the levels usually found in an RAS (>200 mg/L). Oxygen is also consumed in the creation of nitrate. These bacteria metabolize and oxidise the nitrite (NO 2-) produced by Nitrosomonas and convert it to nitrate (NO 3). This is accomplished by another naturally occurring genus of bacteria referred to as Nitrobacter. Like ammonia, the nitrite produced by the Nitrosomonas bacteria is toxic to aquatic organisms and must be oxidised further to a less toxic form of nitrogen. The bacteria that convert ammonia to nitrite are known collectively by their genus name Nitrosomonas. This is an aerobic process that needs oxygen to occur. This waste product is toxic to the fish and is an environmental stressor that causes reduced appetite, reduced growth rate, and death at high concentrations.įortunately, naturally occurring bacteria oxidise the ammonia, use it to grow, and convert it to nitrite (NO 2-). Finfish excrete ammonia (NH3), mostly from their gills, and it dissolves in the water in which the fish must live. Nitrifying bacteria process dissolved nitrogenous waste products excreted by the aquatic organisms being cultured.Īll cultured organisms, vertebrates or invertebrates, finfish or shellfish, produce waste as a result of the nutrition they receive. The biofilter houses the nitrifying bacteria and is the primary site where biological nitrification occurs. The biological filter, or biofilter, is a key component in the filtration portion of a recirculating aquaculture system (RAS).
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