Acta agriculturae Slovenica, 118/3, 1–4, Ljubljana 2022 doi:10.14720/aas.2022.118.3.2488 Short scientific article / kratki znanstveni prispevek Ultraviolet disinfection of water in recirculating aquaculture system: a case study at sturgeon caviar fish farm Anatolіі SEMENOV 1, 2, Kateryna SEMENOVA 3 Received December 30, 2021; accepted July 04, 2022. Delo je prispelo 30. decembra 2021, sprejeto 04. julija 2022 1 Poltava University of Economics and Trade, Faculty of Commodity science, Trade and Marketing, Department of Commodity research, Biotechnology, Expertise and Customs, Poltava, Ukraine 2 Corresponding author, e-mail: asemen2015@gmail.com 3 Poltava University of Economics and Trade, BA in International Economics, Master`s degree student Ultraviolet disinfection of water in recirculating aquaculture system: a case study at sturgeon caviar fish farm Abstract: In this report, we present a practical example of ultraviolet (UV) water disinfection in an aquaculture facility for sturgeon caviar production. Among the methods of water disinfection in recirculating aquaculture systems, the technical approaches using ozonation or ultraviolet radiation in com- bination with other methods are the most effective. However, improper use of ozonation can result in excessive ozone con- centrations that can cause serious harm to fish and be harm- ful to the environment and personnel. Therefore, we describe an example of a reagent-free ultraviolet water disinfection system. Preliminary results show that filtration followed by ultraviolet irradiation inactivates microorganisms in fish tank water. Total microbial count, total coliform bacteria, and E. coli (CFU/m3) did not exceed the permissible values. The described UV system provides an irradiance of 180 W/m2. For a pool with a water volume of 300 m3, bacteriological purity of the water was achieved with 480 W of UV-light. Key words: aquaculture; fish; sturgeon; recirculation sys- tem; UV water disinfection Razkuževanje vode z ultravijolično svetlobo v recirkulacij- skem akvakulturnem sistemu reje: primer ribogojnice jese- trov za prirejo iker, namenjenih za proizvodnjo kaviarja Izvleček: V članku predstavljamo primer razkuževanja vode z ultravijolično (UV) svetlobo v recirkulacijskem akva- kulturnem sistemu reje jesetrov za prirejo iker, namenjenih za kaviar. Med metodami razkuževanja vode pri gojenju rib v zaprtih akvakulturnih sistemih reje so najučinkovitejši pristopi z uporabo ozoniranja ali UV sevanja v kombinaciji z drugimi metodami. Nepravilna uporaba ozoniranja za razkuževanje vode lahko povzroči nastanek prevelikih koncentracij ozona, ki lahko negativno vplivajo na zdravje rib in škodujejo okolju in osebju v ribogojnici. Predstavljamo primer razkuževanja vode, ki temelji na uporabi UV svetlobe. Preliminarni rezultati so pokazali, da razkuževanje vode z metodo filtracije in UV ste- rilizacije zagotavlja učinkovito inaktivacijo mikroorganizmov v bazenu za gojenje rib, saj skupno število mikrobov, skupno število koliformnih bakterij in E. coli (CFU/m3) ni preseglo pri- poročenih vrednosti. Opisani sistem proizvaja jakost UV seva- nja 180 W/m2, kar ob uporabi 480 W kvarčnih UV žarnic zago- tavlja bakteriološko čistost vode za bazen prostornine 300 m3. Ključne besede: akvakultura; ribogojstvo; ribe; jeseter; recirkulacijski sistem; razkuževanje vode; UV svetloba Acta agriculturae Slovenica, 118/3 – 20222 A. SEMENOV and K. SEMENOVA 1 INTRODUCTION In recent years, in Ukraine, as in other countries, industrial farming methods in aquaculture facilities have become increasingly important. These include fish farming in recirculating aquaculture systems (RAS) (Martins et al., 2010; Bulc et al., 2011). This approach can achieve high growth rates with minimal energy costs (Zainal et al., 2021) and is economically advanta- geous because of the reuse of water resources and the possibility of optimizing the hydrochemical regime without depending on environmental conditions. The development of aquaculture farms and the as- sociated increase in production volume has led to prob- lems with effective disinfection of water in RAS. The choice of the method and means of purification of recy- cled water is of crucial importance for the technological cycle of fish farming. New technologies offer alterna- tives to classical water treatment methods (e.g., parti- cle filtration, biofiltration, and gas exchange) (Huyben et al., 2018). Gundula et al. (2019) consider recircula- tion systems as systems that incorporate a number of water purification stages, which consists of: 1) devices for removing solid particles from water, 2) biofilters for ammonia reduction, and 3) gas exchange devices for carbon dioxide removal and oxygen addition. Rearing fish in RAS may be beneficial for increased fish survival rates, when compared to standard cage systems, mostly due to stable microbial environment that prevents op- portunistic microbe multiplication (Dahle et al., 2020). UV irradiation and ozonation are the most com- mon methods of water disinfection in aquaculture. Studies have shown that it is possible to achieve opti- mal conditions for the microbiological composition of water also with the combined effects of filtration, UV radiation, and ozonation (Gregersen et al., 2020; Mid- dlemiss et al., 2015). The effectiveness of these methods, as well as their combination depends on the presence of dissolved and suspended organic compounds in the water (Semenov et al., 2021a). Overexposure to ozone can cause serious damage to fish and can be harmful to the environment (Sharrer et al., 2005). During ozone treatment, microparticles are broken down into molec- ular structures and then removed at different stages of filtration. This method of water purification is suitable for fish incubators that are sensitive to microparticles and bacteria in the water. However, there are arguments against the use of ozonation in RAS (Attramadal et al., 2012) as such systems require a large amount of ozone, which is mostly consumed in the reactions with organic substances, however residual ozone and reaction by- products can be toxic for fish and live feed. On the other hand, UV irradiation of water is considered a safe alter- native to ozonation. When using ultraviolet radiation, the number of microorganisms is significantly reduced (Moriarty et al., 2018) as it inactivates microorgan- isms through photochemical reactions of nucleic acids, which occurs in a special ultraviolet chamber (Semenov et al., 2018) with no harmful effects on fish, environ- ment, and personnel. According to Runia (1995), different irradiances are required for different types of microorganisms: for inactivation of bacteria and fungi from 100 mJ/cm2 and for viruses from 250 mJ/cm2. These relatively high doses compensate for the possible change in turbidity of the water and the change in transmittance of UV ra- diation energy. For example, Sharrer et al. (2005) used UV doses ranging from 75 to 1800 mW/cm2 to achieve inactivation of coliform bacteria in rearing salmonids. However, the inactivation process is not guaranteed if suspended solids are present in the water stream. In practice, radiation intensity of at least 400 mJ/m2 is re- quired for the operation of fish incubators and RAS. In Ukraine, ozonation is the predominant method of water disinfection in aquaculture (Semenov et al., 2021a; Se- menov et al., 2021b). In this report we present an exam- ple of an alternative solution – UV disinfection of water in aquaculture facility for caviar production. 2 MATERIALS AND METHODS Experimental work was carried out in an aquacul- ture farm (Zhashkov, Cherkasy region) when growing sturgeon (Acipenser gueldenstaedtii) for caviar produc- tion. Fish farming was carried out in an insulated hang- ar. Bioload of the system was 53–55 kg of live fish per 1 m2 of pool area. Fish were fed four times a day using commercial diet. All experimental work was carried out in a closed water supply system with a volume of 300 m3, water temperature of 21–22 °С, pH level of 7.3–7.7, and dissolved oxygen content of 5.6–5.8 mg/l. Water purifi- cation was carried out continuously through the water recirculation channel with width of 200 mm and water flow height of 840-860 mm. The recirculation channel provides a water flow of 75 m3/h. For UV disinfection of water, quartz lamps (type ZW80D19W) were used with the power of 80 W, lamp current of 800–1200 mА, and UV (254 nm) irradiance (d = 1 m) of 240–270 μW/cm2. Presence of bacteria was determined with bacteriologi- cal cultures on dense nutrient media, followed by iden- tification of phenotypic or serological properties of the studied strains. Acta agriculturae Slovenica, 118/3 – 2022 3 Ultraviolet disinfection of water in recirculating aquaculture system: a case study at sturgeon caviar fish farm 3 RESULTS AND DISCUSSION Among the types of UV disinfection units consid- ered, there are two types – surface and submersible. A surface sterilizer consists of a battery of UV lamps set-up above the water. Submersible sterilizers, in which water disinfection takes place in the irradiation chamber are more efficient and reliable (Semenov et al., 2018). In or- der to obtain satisfactory results in terms of water quality it is necessary to continuously treat the water. For this, filtration and bacterial disinfection are used together. For The obtained results of bacteriological studies of water when growing fish are presented in Table 1. Bacteriological studies of the water in the pool showed that ultraviolet disinfection combined with fil- tration provides the necessary bacteriological purity of water in pools with a volume of up to 300 m3. With the proposed system, bacteria causing fish diseases such as Flexibacter Cytophaga, Aeromonas and mycoses (Sapro- legniales) were not detected within first three months and after six months. 4 CONCLUSIONS A reagent-free system for disinfecting water in fish breeding pools based on UV irradiation was assembled and tested. In the case of RAS with a water volume of 300 m3, the proper bacteriological quality of the water was ensured for six monitored months by installing UV quartz lamps with a power of 480 W and a UV irradia- tion intensity of 180 W/m2. 5 REFERENCES Attramadal, K. J. K., Øie G., Størseth, T. R., Alver, M.O., Vad- stein, O., Olsen, Y. (2012). The effects of moderate ozonation or high intensity UV-irradiation on the microbial environ- ment in RAS for marine larvae. Aquaculture, 330, 121–129. https://doi.org/10.1016/j.aquaculture.2011.11.042 Bulc, T. G., Istenic, D., Klemenci, A. K. (2011). The efficiency of a closed-loop chemical-free water treatment system for cyprinid fish farms. Ecological Engineering, 37(6), 873–882. https://doi.org/10.1016/j.ecoleng.2011.01.004 Dahle, S. W., Bakke, I., Birkeland, M., Nordøy, K., Dalum, A. S., Attramadal, K. J. K. (2020). Production of lumpfish (Cy- clopterus lumpus L.) in RAS with distinct water treatments: Effects on fish survival, growth, gill health and microbial communities in rearing water and biofilm. Aquaculture, 522, 735097. https://doi.org/10.1016/j.aquaculture.2020.735097 Gregersen, K. J., Pedersen, P. B., Pedersen, L.-F., Liu, D., Dals- gaard, J. (2020). UV irradiation and micro filtration effects on micro particle development and microbial water qual- ity in recirculation aquaculture systems. Aquaculture, 518, 734785. https://doi.org/10.1016/j.aquaculture.2019.734785 Figure 1: Scheme of the water purification and disinfection installation the purification and disinfection of water for sturgeon fish farming in RAS we assembled a UV irradiation sys- tem schematically presented in Figure 1. The system includes the following: 1) installation for removing coarse dirt, 2) installation for removing highly dispersed impurities (fine cleaning), 3) installation for ultraviolet water disinfection, and 4) equipment for pH correction, water saturation with oxygen, water heating and electronic control system. For the inactivation of mi- croorganisms, a 480 W UV installation has been devel- oped, which consists of six low-pressure ultraviolet lamps with the previously described characteristics. Lamps are placed after the filtration units and fitted vertically within the water flow. They are inserted in quartz glass covers to maximize the irradiation area. The total bactericidal flow is 180 W/m2. Indicator name Requirements (CFU/cm3) Research results (days) 0 7 30 60 90 120 Total microbial count (CFU/cm3 at 37 °C) < 100 17 40 79 52 60 89 Total coliforms (CFU/100 cm3) - - - - - - - E. coli (CFU/100 cm3) - - - - - - - Table 1: The results of bacteriological studies of water in the pool when growing fish Acta agriculturae Slovenica, 118/3 – 20224 A. SEMENOV and K. SEMENOVA Gundula, P., Ianchenko, A., Kotzen, B. (2019). Aquaponics in the Built Environment. In: Goddek, S., Joyce, A., Kotzen, B., Burnell, G. M. (eds.) Aquaponics Food Production Sys- tems: Combined Aquaculture and Hydroponic Production Technologies for the Future. Springer Nature, Switzerland, Р. 619. https://doi.org/10.1007/978-3-030-15943-6 Huyben, D., Bevan, D., Stevenson, R., Zhou, H., Moccia, R. (2018). Evaluation of membrane filtration and UV ir- radiation to control bacterial loads in recirculation aquaculture systems. Aquaculture International, 26(2). https://doi.org/10.1007/s10499-018-0301-z Martins, C. I. M., Eding, E. H., Verdegem, M. C. J., Heins- broek, L. T. N., Schneider, O., Blancheton J. P., ... Verreth, J. A. J. (2010). New developments in recirculating aqua- culture systems in Europe: A perspective on environmen- tal sustainability. Aquacultural Engineering, 43(3), 83–93. https://doi.org/10.1016/j.aquaeng.2010.09.002 Middlemiss, K., Daniels, C., Urbina, M., Wilson, R. (2015). Combined effects of UV irradiation, ozonation, and the probiotic Bacillus spp. on growth, survival, and general fitness in European lobster (Homarus gammarus). Aqua- culture, 444, 99–107. https://doi.org/10.1016/j.aquacul- ture.2015.03.028 Moriarty, M. J., Semmens, K., Bissonnette G. K., Jaczynski J. (2017). Inactivation with UV-radiation and internal- ization assessment of coliforms and Escherichia coli in aquaponically grown lettuce. Lebensmittel-Wissenschaft und-Technologie, 89(2), 624–630. https://doi.org/10.1016/j. lwt.2017.11.038 Runia, W. T. (1995). A review of possibilities for disinfection of recirculation water from soilless culture. Acta Horticul- turae, 382, 221–229. https://doi.org/10.17660/ActaHor- tic.1995.382.25 Semenov, А. (2018). Device for disinfection of water by using ultraviolet radiation. 8th International Conference Physics of Liquid Matter: Modern Problems (PLMMP 2018), 18–22 May 2018, Kyiv, Ukraine, Р.1-20. http://dspace.puet.edu.ua/ handle/123456789/9287 Semenov, А., Vyzhva S., Sakhno T., Semenova N. (2021a). Com- bined method of UV treatment and ozonation during water disinfection in swimming pools. XV International Scientific Conference «Monitoring of Geological Processes and Ecologi- cal Condition of the Environment», 17–19 November 2021, Kyiv, Ukraine, Mon-21-095. http://dspace.puet.edu.ua/ handle/123456789/11527 Semenov, A., Sakhno, T., Sakhno, Y. (2021b). Photobiological safety of lamps and lamp systems in agriculture. Journal of Achievements in Materials and Manufacturing Engineering, 106(1), 34–41. https://doi.org/10.5604/01.3001.0015.0527 Sharrer, M. J., Summerfelt, S. T., Bullock, G. L, Gleason, L. E., Taeuber J. (2005). Inactivation of bacteria using ul- traviolet irradiation in a recirculating salmonid cul- ture system. Aquacultural Engineering, 33(2), 135–149. https://doi.org/10.1016/j.aquaeng.2004.12.001 Zainal, A. G., Yulianto, H., Rudy, Yanfika, H. (2021). Finan- cial benefits of the environmentally friendly aquaponic media system. IOP Conference Series: Earth and Environ- mental Science, 739, 012204. https://doi.org/10.1088/1755- 1315/739/1/012024