Can ClO₂ pre-oxidation reduce the byproduct formation and toxicity of the water treated by the UV/chlorine process?

The UV/chlorine process is an emerging advanced oxidation process (AOP) that produces a number of reactive species (e.g., hydroxyl radicals and reactive chlorine species) for micropollutant abatement. However, undesired chlorinated byproducts are generated in this process and may consequently increase the toxicity of the treated water. Pre-oxidation by chlorine dioxide (ClO2) has been reported to reduce byproduct formation in the post-chlor(am)ination process, and it is hypothesized to be able to reduce the byproduct formation and toxicity of the water treated by the UV/chlorine process. In the synthetic drinking water containing 2.0 mg C/L of Suwannee River Natural Organic Matter (SRNOM) and buffered at pH 7.5, the pre-oxidation by 1.0 mg/L of ClO2 for 30 min decreased the concentrations of total organic chlorine (TOCl), six volatile disinfection byproducts, and two haloacetic acids by 28%, 27%, and 19%, respectively, in the post-UV/chlorine process, compared to those without pre-oxidation. The suppressing of the formation of these organic byproducts was more significant at a higher ClO2 dosage, a longer pre-oxidation time, and a lower pH. On the other hand, the ClO2 pre-oxidation increased the concentration of chlorate by 25% compared to the case without pre-oxidation. Interestingly, the ClO2 pre-oxidation reduced the genotoxicity and cytotoxicity of the treated water by the UV/chlorine process by 30% and 24%, respectively. Characterizing the changes of SRNOM properties and correlating SRNOM changes with byproduct formation and toxicity changes are on-going and will be presented and discussed.