Enhancement effect among a UV, persulfate, and copper (UV/PS/Cu2+) system on the degradation of nonoxidizing biocide: The kinetics, radical species, and degradation pathway

Abstract Reverse osmosis concentrate (ROC) generally contains highly toxic and biorefractory organic pollutants. In this study, various oxidation systems, including UV, persulfate (PS)/Cu 2+ , UV/PS, and UV/PS/Cu 2+ , were evaluated for the degradation of nonoxidizing biocides, which are commonly used in reverse osmosis systems for preventing biofouling. The results showed that UV/PS/Cu 2+ had an enhancement effect among UV, PS, and Cu 2+ . Compared with UV/PS, the degradation efficiency of UV/PS/Cu 2+ increased 4.4%–22.2% for dodecyl trimethyl ammonium chloride (DTAC) and 19%–37.6% for dodecyl dimethyl benzyl ammonium chloride (DDBAC). The k obs of DTAC and DDBAC by UV/PS/Cu 2+ were approximately 1.5–2 times higher than those of the UV/PS system, which were examined to be 0.569 and 0.602 min −1 , respectively. The contributions of SO 4 •− , HO • , and other way on the degradation of DTAC and DDBAC in the UV/PS/Cu 2+ system were observed to be 77.0%, 1.0%, and 22.1% for DTAC and 55.3%, 1.0%, and 12.0% for DDBAC, respectively, at pH 7. The effect of humic acids (HAs) and natural organic matter (NOM) considerably impeded the degradation of DTAC (50 and 54%) and DDBAC (47 and 69%) when the concentration of HAs and NOM was 1 and 10 mg/L, respectively. The degradation of DTAC by various metals was enhanced in the order Cu 2+ > Fe 2+ > Mg 2+ > Mn 2+ at 0.1 mg/L, whereas that of DDBAC was Cu 2+ > Mg 2+ > Zn 2+ > Fe 2+ > Mn 2+ .