Kinetics and Mechanism of Sulfamethazine Degradation in Aqueous Solution by Electron Beam Irradiation: Influence of Hydrogen Peroxide Addition

Sulfamethazine (SMZ), a widely used sulfonamide antibiotic, frequently occurs in aquatic environments and resists removal by conventional treatment methods. This study investigates the degradation kinetics, mechanistic pathways, and mineralization behavior of SMZ in aqueous solution under electron beam irradiation, with emphasis on the influence of hydrogen peroxide (H2O2). SMZ degradation followed pseudo-first-order dose kinetics across all tested conditions, with dose constants decreasing from 4.6 to 2.7 kGy−1 as initial concentration increased (10–30 mg/L). pH strongly affected reactivity, with the highest degradation rate under acidic conditions. Reactive species studies confirmed that SMZ degradation is overwhelmingly governed by hydroxyl radicals (•OH), with the reactivity hierarchy •OH hydrogen atoms (•H) hydrated electrons . The addition of H2O2 (10–30 mg/L) significantly enhanced initial degradation rates and increased dose constants up to 6.3 kGy−1 by generating supplementary •OH through radiolytic decomposition. TOC measurements indicated partial mineralization, with more pronounced TOC removal in the presence of peroxide, confirming deeper oxidation of persistent intermediates. Nine major transformation products were identified by LC-MS, supporting a degradation mechanism involving hydroxylation, desulfonation, heterocyclic ring cleavage, and progressive oxidation toward smaller organic acids and inorganic ions. ECOSAR predicts low aquatic toxicity for most intermediates, whereas one (P8) is predicted to be toxic. Overall, the findings demonstrate that electron beam irradiation, especially when coupled with H2O2, is an effective and high-rate advanced oxidation technology for SMZ degradation and offers valuable insights for its application in wastewater treatment.