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This study investigated the transformation of triclosan (TCS) following co-exposure to UV irradiation and ClO 2 . 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-Cl 2 DD) was not detected. The TCS degradation was sensitive to ClO 2 dosage, pH, H 2 O 2 , and natural organic matter (NOM), but not to the carbonate (CO 3 2- ) 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 2 concentration increased from 0.25 to 1.5 mg L -1 . TCS degradation can be promoted at low NOM level (1, 3, and 5 mg L -1 ), whereas was inhibited at high NOM concentrations of 7 and 9 mg L -1 . While adding H 2 O 2 , the degradation rate of TCS increased with increasing H 2 O 2 concentration from 1 to 3 mg L -1 ; however, too low or overdosed H 2 O 2 (0.5 and 5 mg L -1 ) hindered TCS degradation. Based on the results of a microtox bioassay, the toxicity did not change following the co-exposure process.

The UV/ClO2 process for triclosan ( TCS) removal was studied. The influences of several factors such as the initial pH, dose of ClO2, initial concentration of TCS and humic acid( HA) on TCS degradation in the UV/ClO2 combined process were discussed. The results showed that the UV/ClO2 process could effectively remove TCS and had a synergistic effect. When the light intensity was 6.5 μW x Cm(-2), the dose of ClO2 was 0. 5 mg x L(-1) and the concentration of TCS was 300 μg x L(-1), when UV and ClO2 were applied alone, the TCS removal rates within 1 min were only 5.23% and 84.93% respectively. The removal rate reached up to 99.13% after 1 min degradation using the UV/ClO2 combined process. In test conditions ( pH 6-9), the removal rate increased from 99.4% to 99. 63% with the increase of pH. Increasing dose of CIO2 could promote TCS removal. When the dose of ClO2 was 0.5-1.5 mg x L(-1), the removal rate was increased from 98.1% to 99.89%. The initial concentration of TCS was negatively correlated with the removal rate. When the initial concentration increased from 100 - 500 μg x L(-1), the removal rate of TCS was decreased from 99.98% to 94.39%. Low concentration of humic acid was beneficial to the removal of TCS, and high concentration of it had the opposite effect. Degradation products of TCS were investigated by GC/MS. Degradation of TCS by the processes of UV, ClO2 and UV/ClO2 also indicated that the main degradation products of the TCS were 2, 4-dichlorophenol (2,4-DCP), 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD), etc.