Analysis of Applying Surface Water Treatment Technology When Using Chlorine Dioxide at Water Supply Plants

Abstract

The results of the conducted research made it possible to establish that in EU countries chlorine dioxide (CD) is more often used for secondary or final disinfection of drinking water. By-products of this process are chlorites and chlorates, which are subject to control in the drinking water of all EU countries. Aldehydes and carboxylic acids can also be formed in drinking water, which leads to a decrease in the microbiological stability of tap water. Ozonation and filtration using a carbon filter are used in the final stage of drinking water purification, which contributes to a significant reduction in the dose of CD and water contamination with toxic chlorites. In the case of pre-oxidation of water with sodium hypochlorite, the largest amount of chlorites and chlorates is formed, while in the case of using potassium permanganate for the same purpose, the need for CD and the amount of chlorites and chlorates in drinking water reduced. Chlorination of natural water that has undergone CD pre-oxidation leads to complete oxidation of the chlorites that have formed, increases the effectiveness of disinfection, and provides a bacteriostatic effect in the distribution network. During 2021-2022, when using CD for the treatment of drinking water at the Dniprovska WTP in Kyiv it was established that the process of treating natural water with CD is accompanied by the formation of its by-products, mainly toxic chlorites, the levels of which depend on the applied doses of CD and are the lowest in winter, while the largest ones are observed in summer and do not always reach regulatory values (0,2 mg/l) and range up to 0,7 mg/l, which corresponds to the WHO recommended standard for this substance in drinking water. Italian scientists focus their attention on the fact that during the first years of using CD at each water supply station, optimal conditions must be ensured for the safe and effective use of this reagent. Therefore, CD is becoming widespread in the EU countries and Ukraine for the treatment of tap drinking water; it is an alternative method of water effective disinfection at water supply stations with traditional surface water purification technology. Using such a method for treating surface water requires a preliminary pilot experiment and should be carried out along with an analysis of the feasibility of using the methods for preliminary and/or final purification of drinking water from organic substances and additional disinfection. Today, based on experimental and natural studies, it is relevant to expand knowledge about the properties of CD in the case of its use in drinking water supply for the treatment of surface water with a high content of organic substances.