Degradation of chlorinated and hydroxylated intermediates in UVA/ClO2 systems: A chlorine-based advanced oxidation process investigation

Abstract

The chlorination used in water treatment plants can promote the formation of toxic compounds, which can be minimized by substituting free available chlorine (FAC) with chlorine dioxide (ClO2). Besides disinfection, combining ClO2 with UV radiation leads to the efficient elimination of organic substances. This work employed a lab-made reactor equipped with LEDs emitting at 367 nm with adjustable photon flux to investigate the efficiency of the UVA/ClO2 process and the formation of hydroxylated and chlorinated products during the degradation of phenol and coumarin. The degradation of coumarin was investigated in a central composite design and depended on the ClO2 concentration and pH. Increasing the ClO2 concentration was necessary to promote the degradation. In higher ClO2/phenol ratios, 80% of the total phenolic compounds were removed at pH 3, 5.5, and 8. The mineralization efficiency increased with the pH, along with the concentration of chlorinated compounds, indicating these products are more persistent than the hydroxylated ones. The UVA/ClO2 process was advantageous in removing and mineralizing phenol and coumarin if compared to direct oxidation, but the process needs to be improved to minimize the formation of chlorinated organic products, and elimination of ClO2- and ClO3- requires post-treatment method.