Effects of pre-oxidation by ClO₂ and post-treatment by the UV/chlorine process on the DBP formation in the drinking water treatment

The UV/chlorine process has been used for treatment of recalcitrant micropollutants, yet the formation of disinfection byproducts (DBPs) is of concern. Pre-oxidation by ClO2 can mitigate DBP formation in the post-chlor(am)ination, and it is anticipated to be able to reduce the DBP formation in the post-UV/chlorine process as well. This study evaluated the impacts of integrating the ClO2 pre-oxidation and the UV/chlorine process with the conventional treatment units (CTUs, Figure 1) on the DBP formation in synthetic drinking water containing Suwannee River Natural Organic Matter (SRNOM). Concentrations of volatile DBPs (e.g., trihalomethanes, haloacetonitriles), haloacetic acids (HAAs), chlorite, and chlorate were measured after each unit (Figure 1). Volatile DBPs and HAAs were mainly formed in the post-UV/chlorine process, and their concentrations were reduced by 32.9% and 55.5%, respectively, by ClO2 pre-oxidation. The reduced DBP formation was attributed to the consumption of DBP precursor moieties by ClO2, as demonstrated by the continuous decreases in the fluorescence intensity of SRNOM in fulvic and humic-like regions after each unit. Around 3.4 µg/L chlorite and 17.0 µg/L chlorate were collectively formed in the integrated process train, where chlorite formed in the ClO2 pre-oxidation process (0.7 mg/L) could be further oxidized to chlorate in the post-UV/chlorine process. The formation of brominated DBPs and bromate in the integrated treatment train in the presence of bromide ions are being investigated and will be discussed and presented.