Degradation of carbamazepine by the UVA-LED/ClO/NaClO process: Kinetics, mechanisms and DBPs yield.

A mixed oxidant of chlorine dioxide (ClO) and NaClO was often used in water treatment. A novel UVA-LED (365 nm)-activated mixed ClO/NaClO process was proposed for the degradation of micropollutants in this study. Carbamazepine (CBZ) was selected as the target pollutant. Compared with the UVA/ClO process, the UVA/ClO/NaClO process can improve the degradation of CBZ, with the rate constant increasing from 2.11×10 sec to 2.74×10 sec. In addition, the consumption of oxidants in the UVA/ClO/NaClO process (73.67%) can also be lower than that of UVA/NaClO (86.42%). When the NaClO ratio increased, both the degradation efficiency of CBZ and the consumption of oxidants can increase in the UVA/ClO/NaClO process. The solution pH can affect the contribution of NaClO in the total oxidant ratio. When the pH range of 6.0-8.0, the combination process can generate more active species to promote the degradation of CBZ. The change of active species with oxidant molar ratio was investigated in the UVA/ClO/NaClO process. When ClO acted as the main oxidant, HO• and Cl• were the main active species, while when NaClO was the main oxidant, ClO• played a role in the system. Both chloride ion (Cl), bicarbonate ion (HCO), and nitrate ion (NO) can promote the reaction system. As the concentration of NaClO in the reaction solution increased, the generation of chlorates will decrease. The UVA/ClO/NaClO process can effectively control the formation of volatile disinfection by-products (DBPs), and with the increase of ClO dosage, the formation of DBPs can also decrease.