Degradation behavior of triclosan by co-exposure to chlorine dioxide and UV irradiation: influencing factors and toxicity changes.

This study investigated the transformation of triclosan (TCS) following co-exposure to UV irradiation and ClO. Special attention was given to understand the influencing of water quality parameters and toxicity changes during the co-exposure process. The results show that the co-exposure process prompted TCS elimination quickly and effectively, with more than 99% of TCS degraded under the experimental conditions. The molar yield ratios of 2,4-dichlorophenol/TCS (2,4-DCP/TCS) were calculated to be 35.81-74.49%; however, the by-product of 2,8-dichlorodibenzop-dioxin (2,8-ClDD) was not detected. The TCS degradation was sensitive to ClO dosage, pH, HO, and natural organic matter (NOM), but not to the carbonate (CO) concentration. Neutral and slightly alkaline condition were favorable to TCS elimination. The TCS removal rate increased from 85.33 to 99.75% when the ClO concentration increased from 0.25 to 1.5 mg L. TCS degradation can be promoted at low NOM level (1, 3, and 5 mg L), whereas was inhibited at high NOM concentrations of 7 and 9 mg L. While adding HO, the degradation rate of TCS increased with increasing HO concentration from 1 to 3 mg L; however, too low or overdosed HO (0.5 and 5 mg L) hindered TCS degradation. Based on the results of a microtox bioassay, the toxicity did not change following the co-exposure process.