Synergistic effect of nitrate on UV-chlorine photochemical degradation of carbamazepine

Abstract

We investigated the use of UV-chlorine advanced oxidation process for the removal and transformation of carbamazepine (CBZ), and its photochemical synergy with NO₃^- for the production of ^.OH towards enhancing CBZ removal in aqueous solution. Production of ^.OH by UV-chlorine system with/without NO₃^- was studied under different conditions, by using salicylic acid (SA) as the chemical probe for ^.OH. Initial concentration of 30 mg/L SA, 5 and 10 mg/L chlorine, and 0-10 mg/L NO₃^- under irradiation at 254 nm (3.026 W/L) in a photochemical reactor was used. Aqueous solutions containing 10 mg/L chlorine and spiked with 4 mg/L NO₃^- gave the highest reproducible generation of ^.OH. Using initial concentrations of 10 mg/L CBZ and 10 mg/L chlorine, 60 % CBZ was removed after 10 min of irradiation without NO₃^-, while 72 % CBZ was removed with 4 mg/L NO₃^- added. There was no noticeable CBZ removal after 10 min of irradiation in the presence of NO₃^- without chlorine. Corresponding dark reactions were also conducted, with no noticeable degradation of CBZ. Samples were analyzed via UHPLC, LC-MS, and TOC (total organic carbon) analyzer for CBZ and TOC concentrations respectively. Although, there was significant reduction in CBZ concentration during both photochemical degradation processes, the was low TOC removal (~10%) in each case. The two photochemical degradation processes also seem to generate similar degradation products indicating that the addition NO₃^- of the UV-chlorine process might not have changed the degradation mechanism. The results indicate that NO₃^- could act synergistically in a UV-chlorine system to increase CBZ removal and reduce the quantity of free chlorine required to achieve a target removal efficiency. This could facilitate reduction in the potential production of chlorinated byproducts in the system.

Keywords: Carbamazepine degradation; Contaminants of emerging concern; Hydroxyl radicals; UV-chlorine advanced oxidation process; UV-chlorine-NO3 − AOP.