Modeling ClO-NOM Reactions for Predicting Byproduct Formation and Micropollutant Degradation in Surface Water.

Chlorine dioxide (ClO) is a promising alternative disinfectant/oxidant to free chlorine in drinking water treatment, while it reacts with natural organic matter (NOM) to form free chlorine, chlorite ions (ClO), and chlorate ions (ClO) as byproducts. Predicting the ClO consumption and the formation of these byproducts using a kinetic model helps to balance the trade-off between disinfection/oxidation efficiency and byproduct formation. This study establishes a summative equation to describe the reaction between ClO and ClO-reactive moieties in the NOM (CRNOM). The average molar yields of ClO, free chlorine, Cl, and ClO from the reactions between ClO and nine NOM isolates are determined to be 0.576 ± 0.017, 0.258 ± 0.022, 0.141 ± 0.010, and 0.039 ± 0.002 per consumed ClO, respectively. The bimolecular rate constants of CRNOM toward ClO () are comparable among nine NOM isolates (683 ± 57 M·s at pH 7.0). The CRNOM concentrations and increase by 2-fold and 1.3-fold, respectively, as pH increases from 6.0 to 9.0, while pH barely affects the molar yields of inorganic products. A kinetic model is established and enables the accurate prediction of ClO and ClO formation and ofloxacin degradation during ClO oxidation in surface water.