Konontsev S. Multistage biological treatment of recirculating water of industrial fish farms

The dissertation for obtaining degree of a Doctor of Technical Sciences for the Specialty 05.17.21 – Water treatment technology. – National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Kyiv, 2019. Data on nitrification-denitrification technology, which was used in the recycled water treatment of RAS, were systematized; the main reasons for the low removal efficiency of dissolved nitrogen compounds were identified. The dependence of undissolved impurities amount in the water on the quantity and quality of supplied mixed feed was established. The efficiency of mechanical purificationg facilities for the preliminary removal of undissolved contaminants was analyzed; the connection with purification capacity of nitrification facilities was found. The technology of multistage biological treatment of RAS recirculating water was developed based on progressive approaches to the processes of treatment of domestic wastewater and restoration of water quality in fish farming, the method of bioconveyer principle and the concept of integrated multi-trophic aquaculture (IMTA). Thus, in the process of RAS water treatment most of the typical contaminants were transformed into biomass of fodder organisms that are involved in the restoration of the conditions of contaminated water. The use of hydrobionts from different trophic groups in the water purification processes was substantiated in accordance with the bio-conveyer principle and the integrated multi-trophic aquaculture concept. Schemes for transformation of nitrogen and phosphorus-containing pollutants into the purification agents’ biomass during the process of multistage biological treatment of recycled water were developed. Biotechnological expediency in separating processes for the treatment of recycling water from ammonium nitrogen and organic contaminants was substantiated. It was substantiated theoretically and proved experimentally that vascular aquatic plants have high assimilating potential on the nutrient elements. The species that adapt better to contaminated water and are able to remove nitrogen compounds intensively were identified. In the process of experimental research, the rational parameters of the process of removal of ammonium nitrogen in phytoreactor with duckweed were determined. A technique for calculating the structure is proposed and recommendations for starting and operating the phytoactor are developed. The purification power for the ammonium nitrogen of phytoreactor with floating aquatic plants was determined, which, depending on the hydraulic load, the specific biomass per unit area and the lighting regime, is 8-14 mgNH4+/(m3·per day).The influence of illumination intensity and duration on biogenic elements assimilation efficiency by plants in the phytoreactor with duckweeds as well as rational process parameters were determined. Use of gastropods for undissolved contaminants destruction was substantiated; which allows to improve the sedimentary qualities, reducing wastes 2.5-3 times with simultaneous increase of mineralization rate from 10-12% to 45-60%. It was showed, that insertion of gastropods species into the bioreactor with a fibrous carrier "Viya" has provided the oxidation capacity for BOD5 in the range of 80-220 g/(m3·day) with a purification effect of 80-90%. Designs of bioreactors that are adapted for the cultivation of certain groups of purification agents were developed. Purification schemes that provide reuse of water at 95% and above were developed in accordance with the technological features of the main objects of industrial fish farming and the conditions for the formation of pollution of the recirculating water from RAS. Schemes for treatment of recycling water from aquaculture systems for growing catfish, cichlids, salmon and sturgeon were developed. The effectiveness of using the developed treatment technology of recirculating water in the cultivation of the decorative hydrobionts, as well as the endangered and valuable species of ichthyofauna for the purpose of their further introduction into natural water bodies was justified. The economic efficiency of implementation of the developed technology for multistage biological treatment was calculated. The developed technology of multi-stage biological treatment was implemented in the projects of reconstruction and construction of RAS treatment facilities for the purpose of growth of these industrial fish farming objects. Some technological solutions were realized in the design of sewage treatment facilities of the municipal sewage of the settlement and the recreation centre. Key words: biological water treatment, recirculating water, RAS, treatment of Nitrogen and Phosphorus, integrated multi-trophic aquaculture