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3.2. Closed Circuit Aquaculture
It is a farming method mostly used in marine fish hatcheries on land, and it is a method of
using the same water in fish tanks by collecting the water used from the channels and
improving it after some filtration stages. Although the daily fresh water requirement varies
according to the system mechanization, it is between 3-10% of the total water. This method,
which is also used in the production of freshwater fish in many developed countries, is also
used in research centers.
Fig. 2. Closed Circuit Aquaculture Diagram
In closed-circuit aquaculture, which is also the basis of the geothermal production system,
dissolved ammonia compounds originating from the feces of fish in the tanks and inedible
feeds are first passed through a solid waste filter. Then, by biological filtration, dissolved
ammonia is converted to nitrite and nitrate by nitrification. As a result of the removal of
nitrate from the water by aeration of the water, the water is made usable in fish tanks again. In
the geothermal system, at this stage, nitrate water becomes fertilizer for vegetables produced
by hydroponic application in plant tanks (pans), and after nitrate is taken by vegetables, water
becomes available for use in fish tanks again.
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