Purpose. Development of a method for the regeneration of highly porous fillers for biofilters after slagging of their pores with biofilm residues in the process of growing aquaculture objects in recirculating aquaculture systems (RAS). Methodology. Regeneration of fillers was performed with solutions of sodium hypochlorite of different concentrations (2.5%, 1%, 0.5% of active chlorine) after their exploitation for 6 months. The cleaning efficiency was monitored by the difference in fillers weights after cleaning. Findings. According to the study, the use of sodium hypochlorite for cleaning highly porous fillers for biofilters (using an example of porous ceramic filler and foamed glass «JBL Micromec») is efficient and cost-effective. A reduction in the weight of the test samples averaged 12.95% for porous ceramics and 15.01% for foamed glass. Based on the obtained data, aqueous solutions with different concentrations of sodium hypochlorite do not have a pronounced difference in efficiency, respectively; the optimal for use is a 0.5% solution. Originality. The use of highly porous fillers for biofilters has long been unprofitable in fish farming due to the rapid loss of their main advantages - a high specific area per unit volume as a result of micropore slagging with biofilm residues. As a result, complete regeneration of these filter materials was required annually, which, given the significantly higher cost compared to polymeric fillers, made their use unprofitable. The described technique allows the use of porous ceramics and foamed glass, after their restoration, for a long time, with replacement only after mechanical wear. Practical value. The described method allows using highly porous fillers for biofilters in the process of growing aquaculture objects without their main disadvantage - a rapid decrease in efficiency as a result of pore slagging with biofilm residues. Keywords: RAS, biofilter, filler, restoration, sodium hypochlorite.

biofilters yielding different fillers was established. Clarias gariepinus juvenile was selected as the biological test-object. This species is characterized by increased resistance to the influence of nitrogen compounds, although juvenile individuals at the growing stage of 0.5 to 200 g are more sensi ve to hydrochemical factors. At the same me, this species is less suscep ble to the roundfactor compared to tradi onal aquaculture objects cul vated in Ukraine. It allows working with this species in rela vely small model RAS installa ons. According to obtained results, biofilters with different types of substrates for nitrifying bacteria are undergoing the cycle of biological equilibrium with the same rate at the start-up phase of RAS filtra on. The survival and growth rates of theAfrican sharptooth ca ish juveniles were slightly higher compared to the use of floa ng polymer filler due to more op mal hydrochemical parameters during the opera on of RAS with the biofilter fillers. This can be associated with a higher specific surface area as those in the polymer filler. In order to verify the results of the experiment, especially regarding the effects of different biofilter fillers on water quality, biological equilibrium rate and biological purifica on unit performance in RAS and fish survival, it is advisable to con nue the study with an experimental increase of organic loading.

Modern technologies of cultivation of hydrobionts in recirculating aquaculture systems require significant volumes of biological filters (about 10% of the total volume of the fish farming system), which makes it relevant to search for new fillers that would have a larger specific surface area for colonisation by microorganisms than conventional polymer filling, which would reduce the size of the biofilter and, accordingly, the cost of water and electricity for the production of aquaculture products. The purpose of the study was to evaluate the effectiveness of using highly porous foamed glass as a biofilter filler, compared to conventional floating polymer loading. To achieve this goal, a systematic approach to a particular problem and general scientific research methods were used: experiment, modelling, comparison, analysis, synthesis, and generalisation. The model experiment was conducted in the educational and scientific laboratory of the Centre for Aquatic Bioresources and Aquaculture of the National University of Life and Environmental Sciences of Ukraine. Based on the results of the experiment, it was found that the test material has a significantly higher bio-cleaning potential than polymer loading for biofilters. The maximum concentration of ammonia in the water of the recirculating aquasystem for growing sturgeon fish, which is oxidised by a biofilter with 1 dm3 of foamed glass as a filler (32 mg/dm3) during the day, was determined. Calculations of the potential biological load during the cultivation of hydrobionts in the aquasystem were carried out, and it was found that 10 md3 of this filler maintains an optimal level of nitrogen content when growing sterlet fish planting material with a planting density of 41.6 kg/m3 or 84.8 kg/m3 of commercial fish. It is determined that the required volume of the biofilter is reduced by 4.55 times, and the cost of water and energy supply for the operation of the recirculating aquasystem will also be proportionally reduced. Thus, the use of foamed glass as a filler for biofilters of recirculating aquasystems will increase the profitability of fish production at aquaculture enterprises

Purpose.Investigate the possibility of using glucose (С6Н12О6) to stimulate heterotrophic nitrification processes in biofilters and reduce the content of ammonium nitrogen in the water of recirculating aquaculture systems (RAS). Methodology. The object of research was the processes of water purification in biofilters of RAS from nitrogen compounds harmful to fish. The subject of research is the rate of heterotrophic nitrification using glucose as a source of organic carbon to accelerate nitrification processes under conditions of critical ammonium nitrogen content in process water. The research was conducted in four experimental RAS of the Fisheries Laboratory of the Department of Aquaculture of NULES of Ukraine. During the experiment, the concentrations of ammonia-ammonium in the water of aqua systems were artificially increased to 2 mg/dm3 by adding ammonium chloride solution, and 10% glucose solution was added in the proportions of 1 cm3, 5 cm3 and 10 cm3 per 100 dm3 of process water. The content of nitrogen compounds in water was determined using the Ptero Test system (NО2-, NH3/NH4+). Evaluation of the effectiveness of biofiltration in different variants of the experiment was performed on the time of excretion of NH3/NH4+ and the physical condition of sterlet fry (Acipenser ruthenus), which acted as a test object. Findings.The effectiveness of using glucose solution as a biologically active substance to stimulate the excretion of ammonia-ammonium by bacteria of the RAS biofilter has been proved. The rate of decrease of the concentration of NH3-/NH4+ to an acceptable level (below 0.1 mg/dm3) in the experimental systems with 5 and 10 сm3 of glucose per 100 dm3 of water was 5 hours versus 7 hours in the control version and in the experimental system with 1 сm3 glucose per 100 dm3 of water. Originality. A study on the use of glucose to accelerate nitrification processes in biofilters of RAS under conditions of critical ammonia-ammonium content in water was conducted for the first time. PracticalValue. The proposed method of stimulating heterotrophic nitrification solves a number of problems associated with a sharp increase of the content of NH3/NH4+ in process water. The use of this method will allow to reduce the risk of death of cultivated aquatic organisms due to a sharp increase of the concentration of ammonia-ammonium in water during the period of establishment of biological balance or in emergency situations. At the same time, it should be taken into account that heterotrophic bacteria grow much faster than nitrifying ones and may outperform the latter in the competition for substrate area in biofilters, so the use of this method is advisable for a short time, if necessary to release process water from excess ammonia-ammonium. Keywords: RAS, biofilter, glucose, heterotrophicnitrification, sterlet.