Superfast degradation of micropollutants in water by reactive species generated from the reaction between chlorine dioxide and sulfite

Chlorine dioxide (ClO2) is used as an oxidant or disinfectant in (waste)water treatment, whereas sulfite is a prevalent reducing agent to quench the excess ClO2. This study demonstrated that seven micropollutants with structural diversity could be rapidly degraded in the reaction between ClO2 and sulfite under environmentally relevant conditions in synthetic and real drinking water. For example, carbamazepine, which is recalcitrant to standalone ClO2 or sulfite, was degraded by 55%-80% in 10 s in the ClO2/sulfite process at 30-µM ClO2 and 30-µM sulfite concentrations within a pH range of 6.0-11.0. Results from experiments and a kinetic model supported that chlorine monoxide (ClO·) and sulfate radicals (SO4·-) were generated in the ClO2/sulfite process, while hydroxyl radical generation was insignificant. Apart from radicals, dichlorine trioxide (Cl2O3) was generated and largely contributed to micropollutant degradation, supported by experimental results using stopped-flow spectrometry and quantum chemical calculations. The impacts of pH, sulfite dosage, and water matrix components (chloride, bicarbonate, and natural organic matter) on micropollutant abatement in the ClO2/sulfite process were evaluated and discussed. When treating the real potable water, the concentrations of organic (five regulated disinfection byproducts) and inorganic byproducts (chlorite and chlorate) formed in the ClO2/sulfite process were all below the drinking water standards. This study disclosed fundamental knowledge advancements relevant to the reaction mechanisms between ClO2 and sulfite, and highlighed a novel process to abate micropollutants in water and wastewater.