Determination of factors affecting the biological filtration system in industrial aquaculture and methods to increase its efficiency

Industrial fish farming is becoming increasingly developed, and, in particular, the cultivation of aquatic organisms in recirculating aquaculture system (RAS). These systems are promising due to the possibility of growing fish at high planting densities with minimal use of water resources. To bring the circulating waters to the values of indicators necessary for the cultivation of a certain type of fish, equipment is used (mechanical and biological filtration systems, disinfection, aeration, etc.), which allows to maintain the factors of the growing environment at the required technological level. The resource efficiency and performance of the entire system depends on the efficiency of this equipment. One of the most important elements of RAS is a biofilter: the processes of biological oxidation and redox reactions carried out by microorganisms in it make it possible to reduce the concentration of nitrogenous compounds in the system. The main factors influencing the efficiency of the biological filtration system are determined: temperature from 13 to 28 °C, concentration of dissolved oxygen at least 2 mg/l at the outlet of the biofilter, concentration of total ammonium nitrogen up to 4.5 mg/l, pH 8.0–8.2 and the absence of direct sunlight on the open part of the biofilter. RAS makes it possible to control these factors affecting the flow of technological processes. However, the adjustment of the hydrogen index causes difficulties for the service personnel. It is not always possible to make the correct calculation of the required amount of alkali or acid, given the high buffering of circulating waters and to maintain pH values at the same level. In the process of such an adjustment, side chemical compounds are formed, which subsequently need to be removed from the system, increasing the total water consumption of the RAS. There are methods of electrolysis reagentless pH correction. A non-reactive pH corrector with an anode and cathode made of inert bulk materials (graphite) has been developed. Testing of such a system made it possible to correct the values of the hydrogen index of the treated water to pH 6.24±0.114 and 8.10±0.158 at the initial values of 7.4. The processing voltage was 18.3 Volts, Current 2.1 Amperes, with water mineralization (TDS) = 287 ppm. The obtained values make it possible to separate the flows in the system to create favorable conditions for the passage of biotechnological processes in the biofilter, and to influence the ammonia-ammonium balance in fish tanks.

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