Modeling ClO2–NOM Reactions for Predicting Byproduct Formation and Micropollutant Degradation in Surface Water

Chlorine dioxide (ClO 2 ) 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 2 – ), and chlorate ions (ClO 3 – ) as byproducts. Predicting the ClO 2 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 2 and ClO 2 -reactive moieties in the NOM (CRNOM). The average molar yields of ClO 2 –, free chlorine, Cl –, and ClO 3 – from the reactions between ClO 2 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 2, respectively. The bimolecular rate constants of CRNOM toward ClO 2 ( k CRNOM-ClO 2 ) are comparable among nine NOM isolates (683 ± 57 M –1 ·s –1 at pH 7.0). The CRNOM concentrations and k CRNOM-ClO 2 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 2 – and ClO 3 – formation and ofloxacin degradation during ClO 2 oxidation in surface water.