Effect and simulation of CO3·− on the degradation kinetics of sulfamethazine in UV/TiO2 system
Bicarbonate and carbonate ions (HCO3−/CO3^2−) are ubiquitous in wastewater and readily scavenge strong oxidants, leading to the formation of carbonate radicals (CO3·−) in radical-based advanced oxidation processes. This study investigated the influence of HCO3−/CO3^2− on the degradation kinetics of sulfamethazine (SMR) in a UV/TiO2 system. The presence of HCO3−/CO3^2− enhanced the degradation rate of SMR by sixfold compared to UV/TiO2 alone. Radical quenching experiments identified CO3·− as the primary reactive species responsible for the enhanced degradation, with hydroxyl radicals (·OH) also contributing. To quantitatively delineate the roles of reactive species and account for water matrix effects, a kinetic model was constructed using Kintecus software. The model accurately predicted SMR degradation over time and the contributions of individual radicals, demonstrating good predictive capability. Application of the model to real wastewater predicted that CO3·− is the dominant radical responsible for SMR degradation. These findings highlight the critical role of carbonate radicals in UV/TiO2 processes and provide a robust modeling framework for predicting the fate of pharmaceuticals in carbonate-rich waters.