Effects of reductive inorganics and NOM on the formation of chlorite in the chlorine dioxide disinfection of drinking water

Abstract

Chlorine dioxide (ClO₂) disinfection usually does not produce halogenated disinfection by-products, but the formation of the inorganic by-product chlorite (ClO₂^-) is a serious consideration. In this study, the ClO₂^- formation rule in the ClO₂ disinfection of drinking water was investigated in the presence of three representative reductive inorganics and four natural organic matters (NOMs), respectively. Fe²⁺ and S^2- mainly reduced ClO₂ to ClO₂^- at low concentrations. When ClO₂ was consumed, the ClO₂^- would be further reduced by Fe²⁺ and S^2-, leading to the decrease of ClO₂^-. The reaction efficiency of Mn²⁺ with ClO₂ was lower than that of Fe²⁺ and S^2-. It might be the case that MnO₂ generated by the reaction between Mn²⁺ and ClO₂ had adsorption and catalytic oxidation on Mn²⁺. However, Mn²⁺ would not reduce ClO₂^-. Among the four NOMs, humic acid and fulvic acid reacted with ClO₂ actively, followed by bovine serum albumin, while sodium alginate had almost no reaction with ClO₂. The maximum ClO₂^- yields of reductive inorganics (70%) was higher than that of NOM (around 60%). The lower the concentration of reductive substances, the more ClO₂^- could be produced by per unit concentration of reductive substances. The results of the actual water samples showed that both reductive inorganics and NOM played an important role in the formation of ClO₂^- in disinfection.

Keywords: Chlorine dioxide; Chlorite; Disinfection by-products; Natural organic matter; Reductive inorganics.