Hygienic assessment of the main approaches to the use of chlorine dioxide at the water supply plants of Ukraine with surface source of drinking water supply

The purpose of the work. Conduct a hygienic assessment of the main approaches to the use of chlorine dioxide in the water treatment technologies of water supply stations of Ukraine with surface sources of drinking water supply in order to identify and minimize potential risks to human health. Materials and methods of research. The analysis of water purification technologies used at water supply stations in Ukraine for the treatment of drinking water produced from surface sources of drinking water supply was carried out. The results of water quality studies on priority sanitary-chemical and microbiological indicators in the places of drinking water intakes and drinking water, as well as the doses of reagents used for the treatment of drinking water, during 2021-2023. A comparative analysis of the requirements for the quality of drinking water in the case of its treatment with chlorine dioxide, Directive 2020/2184/EU on the quality of water intended for human consumption, national regulations of 22 EU countries and SSRN 2.2.4-171-10 of Ukraine regarding the quality of drinking water. Methods adopted in international practice were used to assess health risks. Research methods: bibliographic, analytical, comparative assessment, sanitary-chemical, microbiological, hygienic assessment, risk assessment, mathematical and statistical. Research results and their discussion. Currently, in the context of the social and political crisis in Ukraine, chlorine dioxide is used at separate water stations in Ukraine with the purpose of: additional final disinfection; additional primary and secondary treatment along with chlorination; primary treatment of water before it enters the water supply station; complete replacement of chlorine gas with chlorine dioxide. Only at the water stations of the Dnipro city of Kyiv and Horishni Plavni city of the Poltava region, chlorine dioxide is used continuously throughout the year for the disinfection of raw water from the surface source of drinking water supply (Dnipro). At the Dnipro water station in Kyiv, the use of chlorine dioxide led to the greatest changes in the technological process of drinking water production and made it possible to ensure its epidemic safety, reduce the amount of dangerous reagents and the content of chlorination and ozonation by-products, as well as ensure the content of toxic chlorites at a level of ≤0.7 mg/l, which corresponds to the permissible human health risk (≤1.0). According to the results of mathematical modeling of the process of formation of chlorites in drinking water, it was determined that the risk of formation of chlorites in the drinking water of the distribution network of the Dnipro water station of the city of Kyiv in excess concentrations will be at the level of ≤1.0, if the total dose of chlorine dioxide is at the level of ≤3.5 mg /l, and the hygienic norm of chlorites is ≤0.2 mg/l. If the hygienic norm of chlorites is adopted at the level of ≤0.7 mg/l, then the risk of formation of excessive chlorite content in the drinking water of the distribution network will decrease by 2.5 times. The current hygienic requirements of Ukraine regarding the content of chlorites (hygienic standard ≤0.2 mg/l) and chlorine dioxide (hygienic standard ≥0.1 mg/l) in drinking water of the distribution network are the strictest compared to the requirements of EU countries and need to be revised. Conclusions. Chlorine dioxide is used in the Ukrainian Armed Forces as a small (15-25 thousand m3/day) and large capacity (100-200 thousand m3/day), most often as an additional or main method of disinfecting drinking water produced from surface, discrete or continuous mode. The risk of excessive chlorite content in the drinking water of the distribution network depends on the total dose of chlorine dioxide and the effectiveness of measures to minimize it. Technologies for the production of drinking water using chlorine dioxide at the water supply station in the city of Horishni Plavni, Poltava region, which involves the use of chlorine dioxide for the treatment of raw water before it enters the water supply station, as well as at the Dnipro water station in the city of Kyiv, which involves the replacement of chlorine gas with preammonization to chlorine dioxide with ferric chloride, allow to optimize the traditional technological process and improve the quality of drinking water in the absence of potential health risks. Keywords. Drinking water, disinfection, chlorites, health risk.