Synergistic effects of UVC and oxidants (PS vs. Chlorine) on carbamazepine attenuation: Mechanism, pathways, DBPs yield and toxicity assessment

The environmental impact and health risk of carbamazepine (CBZ) in water environment has been continuously reported. Ultraviolet C (UVC)/persulfate (PS) and UVC/chlorine (NaClO) processes were confirmed to be able to efficiently eliminate CBZ through the oxidation by reactive radicals (52.82% SO4−· and 44.21% ·OH in UVC/PS system, 53.47% RCS and 43.84% ·OH in UVC/chlorine process, pH 7.0). The second-order rate constants of CBZ reacted with ·OH, SO4−· and RCS were determined to be 8.2 × 109, 9.1 × 108 and 4.2 × 1010 M−1 s−1, respectively. In both processes, increasing oxidants dosage and rising temperature was favorable for elimination, while increasing CBZ concentration retarded its degradation rate. The coexisting of NOM, SO42− and CO32–/HCO3– presented the inhibitory effect, while NO3– promoted the removal. NH4+ exerted an inhibitory effect in UVC/chlorine process, while exerted no obvious influence in UVC/PS system. Cl− posed a promoting role in UVC/PS treatment and a dual effect in UVC/chlorine process. pH affected the quantum yield of chlorine photolysis and the formation of RCS and ·OH. The degradation of CBZ oxidation via UVC/chlorine process was more pH dependent. 12 and 14 CBZ oxidation products were identified in UVC/PS and UVC/chlorine systems, respectively. SO4−·, RCS and ·OH were readily to attack C = C in CBZ molecule, mainly yielding hydroxylated CBZ, epoxy CBZ, pyridine aldehydes and ketones. Of the disinfection by-products (DBPs) assessed, both processes controlled the formation of haloacetic acids, while increased the generation of trichloromethane, especially via UVC/chlorine process. UVC/chlorine process was more economical and effective (EEO UVC/chlorine = 0.2213 kWh L−1), whereas UVC/PS process was safer in terms of DBPs and toxicity control.