Efficient reduction of carbamazepine using UV-activated sulfite: Assessment of critical process parameters and elucidation of radicals involved

Abstract

For a successful reclamation of aquatic systems, advanced reduction processes (ARP) have recently attracted a lot of attention for the elimination of emerging pharmaceutical compounds. This study investigates the synergistic effect between UV and sulfite (UV/sulfite) for the degradation of carbamazepine (CBZ) and elucidates the critical process parameters and degradation mechanisms. No efficient degradation of CBZ is observed when applying sulfite alone, and only little degradation for UV irradiation alone (8.2% in 30 min reaction time), but the combined use of UV/sulfite ARP improves CBZ degradation significantly (99.62% in the same reaction time) through the formation of reductive radicals (eaq−, H, SO3−). The process is demonstrated to follow a pseudo first order kinetic model, with degradation rate constants of CBZ increasing linearly with increasing sulfite dosage and UV irradiance. It is shown that the degradation of CBZ by UV/sulfite is much more favourable in alkaline conditions than in acidic conditions due to the more favourable distribution between SO32− and HSO3−, which are the precursors of the radicals generated during the UV/sulfite process. It is demonstrated that hydrated radicals (eaq−) are responsible for CBZ degradation, excluding the function of hydrogen atoms (H) and sulfite radicals (SO3−). Inhibition experiments, conducted by introducing radical scavengers (NO3− and NO2−) into the system, further demonstrate the crucial contribution of eaq− on the degradation of CBZ. The energy consumption is evaluated for different UV intensities and sulfite concentrations and indicates that a dose of 0.4 mM sulfite in combination with a 18 W UV lamp is the most economic. This study emphasizes the dominant impact of eaq− on CBZ degradation in UV/sulfite-ARP systems and highlights the potential of this process to efficiently eliminate recalcitrant micropollutants in aquatic environments.