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 CO3 2?/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.

Automated summary

The study investigated the efficiency of UV oxidation and chlorine oxidation processes on the treatment of carbamazepine in water, with both methods showing good removal of CBZ. However, the reaction mechanisms differed under different conditions.