Hydrodynamic cavitation/UV oxidation of tetracycline: oxidant-dependent performance of hydrogen peroxide and peroxydisulfate.

A hydrodynamic cavitation/ultraviolet (HC/UV) platform was developed to systematically compare the oxidant-dependent degradation of tetracycline (TC) using hydrogen peroxide (H2O2) and peroxydisulfate (PDS) as oxidants. Cavitation visualization revealed that increasing the inlet pressure enhanced cavity growth and intensified cloud shedding, while TC removal by HC alone was highest at 0.35 MPa within the tested range. Under identical conditions, PDS exhibited a stronger response to binary process coupling than H2O2, with the UV/PDS system showing the highest synergistic index, while the HC/UV/PDS system showed the highest apparent rate constant. Following optimization of oxidant dosage and initial pH, HC/UV/H2O2 and HC/UV/PDS achieved TC removal efficiencies of 98.18% and 96.96%, respectively, within 60 min. The H2O2-assisted system performed more effectively under acidic conditions and exhibited a lower electrical energy per order (EEO) value of 126.52 kWh m-3 order-1 than the PDS-assisted system (143.28 kWh m-3 order-1), indicating slightly more favorable energy performance under the selected conditions. In contrast, the PDS-assisted route demonstrated broader pH adaptability. Scavenger experiments and UHPLC-HRMS/MS analysis indicated oxidant-dependent oxidation behavior. Tentative identification of transformation products suggested that TC degradation predominantly proceeded through oxygenation, side-chain modification, dealkylation, partial skeleton cleavage, and fragmentation. Predictions using the Toxicity Estimation Software Tool indicated that most transformation products exhibited lower estimated acute aquatic toxicity than TC, whereas developmental toxicity and mutagenicity varied with endpoint and product structure. These findings demonstrate that oxidant selection plays a critical role in governing process synergy, degradation pathways, toxicity evolution, and energy efficiency in HC/UV-based advanced oxidation systems, providing valuable insights for the treatment of refractory antibiotic-containing wastewater.