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)/Cu2+, UV/PS, and UV/PS/Cu2+, 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/Cu2+ had an enhancement effect among UV, PS, and Cu2+. Compared with UV/PS, the degradation efficiency of UV/PS/Cu2+ increased 4.4%–22.2% for dodecyl trimethyl ammonium chloride (DTAC) and 19%–37.6% for dodecyl dimethyl benzyl ammonium chloride (DDBAC). The kobs of DTAC and DDBAC by UV/PS/Cu2+ 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 SO4−, HO, and other way on the degradation of DTAC and DDBAC in the UV/PS/Cu2+ 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 Cu2+ > Fe2+ > Mg2+ > Mn2+ at 0.1 mg/L, whereas that of DDBAC was Cu2+ > Mg2+ > Zn2+ > Fe2+ > Mn2+.