Novel solar/sulfite advanced oxidation process for carbamazepine degradation: Radical chemistry, transformation pathways, influence on disinfection byproducts and toxic changes

Abstract

Advanced oxidation processes (AOPs) play a significant role in the elimination of micro-contaminants persistent in water, but challenges remain due to the high input of energy to initiate the AOPs. Herein, an AOP of integrating solar and sulfite autoxidation (solar/sulfite process) was developed to degrade carbamazepine (CBZ). Results revealed that solar/sulfite process was effective in eliminating CBZ. Sulfate and hydroxyl radicals (SO4•− and •OH) generated through radical chain reactions of sulfite autoxidation under solar irradiation contributed to 74.4% and 25.6% of CBZ degradation, respectively, based on the radical quenching tests, electron spin resonance (ESR) detection, and competition kinetics. Reaction pH exhibited significant effect on the CBZ degradation in solar/sulfite process, and the CBZ degradation was favored in neutral and alkaline conditions. The presence of bicarbonate (HCO3–) and humic acid (HA) retarded the CBZ degradation in solar/sulfite process, while chloride (Cl−) had negligible effect on the CBZ degradation. Integrating the UPLC-MS/MS analysis and the condensed Fukui function (CFF) calculation, five major degradation intermediates of CBZ were identified and the transformation pathway was proposed. Applying solar/sulfite as a pretreatment, the formation of disinfection byproducts (DBPs) during subsequent chlorination was significantly reduced, demonstrating its tremendous potential in eliminating micro-contaminants and controlling DBPs formation. The variation of acute toxicity throughout the solar/sulfite pretreatment and post-chlorination was recorded by the behavior of zebrafish larvae. It was found that CBZ degradation in solar/sulfite process led to its detoxification, while the increased acute toxicity during post-chlorination was a remind for the necessity of optimizing the disinfection steps to further reduce the formation of DBPs when solar/sulfite process was in practical applications.