Improvement of monitoring requirements over the application of chlorine-containing agents for water decontamination

Abstract

Introduction. Oxidizing methods are most widely used for water disinfection with such reagents as chlorine, chlorine dioxide, sodium, and calcium hypochlorite. However, the regulatory instruments of the sanitary and epidemiologic legislation do not fully reflect the requirements for monitoring of their use. Materials and methods. We analyzed the research, regulatory and methodological literature concerning water disinfection issues in the process of water treatment and the parameters of water disinfection efficiency as well as the quality of drinking water of three water treatment stations based on production control data (Perm, Russia) and the results of own research (the towns of Nizhny Tagil (Russia) and Curitiba (Brazil)). Results. A comparative analysis of regulatory documents governing the parameters of the efficacy and safety of drinking water disinfection with chlorine in different years showed that, after the completion of the disinfection process of drinking water, residual free chlorine should be kept within 0.3–0.5 mg/L after 30 minutes of contact or residual bound chlorine – within 0.8–1.2 mg/L after 60 minutes of contact. With the simultaneous presence of free and bound chlorine in water, their total concentration should not exceed 1.2 mg/L. When analyzing the production control data for drinking water in the city of Perm, where chloramination was used for water treatment, we established that the concentration range of 1.04–1.44 mg/L of only the residual bound chlorine ensured high efficiency of water disinfection according to microbiological indicators. The examples of water treatment plants in the towns of Nizhny Tagil and Curitiba demonstrated that water treatment with 0.3 and 0.4 mg/L of chlorine dioxide formed no new dangerous organochlorine compounds but the disinfected drinking water contained residual amounts of chlorine dioxide, as well as chlorite and chlorate anions. Conclusion: These indicators should be included in the regulatory documents to monitor the safe use of chlorine dioxide for water disinfection.