Monitoring of the content of dangerous chlorites in drinking water and the efficiency of their removal using the traditional technology of chlorine dioxide water preparation
Authors:   State Institution "O.M. Marzіeiev Institute for Public Health of the NAMSU", Prokopov V.О. , Lypovetska О.B. ,   State Institution "O.M. Marzіeiev Institute for Public Health of the NAMSU", Kulish T.V. ,   State Institution "O.M. Marzіeiev Institute for Public Health of the NAMSU", Sobol V.A. ,   State Institution "O.M. Marzіeiev Institute for Public Health of the NAMSU"
Published: December 2024

Objective. To investigate the features and levels of dangerous chlorites formation when applied in the modernized traditional technology of preparation of drinking water from a surface source of chlorine dioxide and to evaluate its ability to minimize chlorites to safe levels.

Research materials and methods. An analysis of three-year (2021-2023) studies of the use of chlorine dioxide in the modernized traditional two-stage technology for the preparation of drinking water from a surface source (Dnipro River) was performed. The studies included the assessment of drinking water according to sanitary-chemical and microbiological indicators for compliance with DSanPiN 2.2.4-171-10 «Hygienic requirements for drinking water intended for human consumption», and the determination of chlorine dioxide and its by-product - chlorites.
Determination of the content of chlorine dioxide and chlorites in water was carried out by the laboratory of the Dnipro water supply using the ion chromatography method, and by us (separate samples) using the titrimetric method according to Lurie.

Results. It is shown that the traditional two-stage technology for preparing drinking water from a surface source, in which chlorine is replaced by chlorine dioxide, ensures epidemic safety and chemical harmlessness of drinking water in the process of purifying the source water. But it is accompanied by the formation of dangerous by-products in it, in particular, toxic chlorites.
The levels of chlorine dioxide in water are subject to the dose-time (seasonal) dependence and the composition of the source water in terms of organic substances and its temperature regime inherent in each season. They are the smallest in the cold season and the largest in the warm season.
At these doses of chlorine dioxide, the calculated concentrations of chlorites in water, taking into account 50-70% of their formation from every 1.0 mg of chlorine dioxide, were: in winter 0.87-1.21 mg/dm3, in spring - 0.89-1.24 mg /dm3, in summer – 1.23-1.72 mg/dm3, in autumn – 1.35-1.89 mg/dm3, which is 5-10 times more than the national standard (0.2 mg/dm3) and should be minimized to safe levels by water treatment technology.
It was established that with the applied water purification technology, which includes coagulation (aluminum sulfate and ferric chloride), settling and filtering, removal of chlorine dioxide from water in all seasons of the observation years occurs by no less than 90%, which ensured their content in drinking water at the level standard accepted by us (≤ 0,1 mg/dm3).
Against this background, the efficiency of chlorite removal from water according to average annual data did not ensure the content of chlorites in drinking water, in particular in the warm period of the year, at the level of the national standard (0.2 mg/dm3), but never exceeded the standard (0.7 mg/dm3), recommended by WHO.

Conclusions. Studies at the water treatment facilities of the Dnipro water supply in Kyiv have shown that the use of chlorine dioxide is accompanied by the formation of dangerous chlorites in natural water.
At the same time, it is shown that with water treatment technologies that include coagulation (aluminum sulfate and iron chloride), settling and filtering, the levels of chlorine dioxide and chlorites decrease, although in the warm period of the year, chlorites can exceed the national standard in drinking water by 2-3 times.
The expediency of recommending the Ministry of Health of Ukraine to change the norm of chlorites in drinking water from 0,2 mg/dm3 to 0,7 mg/dm3, which is used today in European countries, is scientifically justified.