Multiple production of highly active particles for oxytetracycline degradation in a large volume strong ionization dielectric barrier discharge system: Performance and degradation pathways

In this study, the degradation of oxytetracycline (OTC) in aqueous solution by humid O2 strong ionization dielectric barrier discharge (DBD) with a 2.2 t/h large volume was investigated. Based on the electron spin resonance (ESR) results and the detection of O3 and H2O2 concentrations, the existence of high concentrations of hydroxyl radicals (center dot OH) (0.85 mmol/L), O3 (14.2 mg/L), and H2O2 (63.3 mg/L) produced via humid O2 strong ionization discharge DBD was verified. In addition, the effects of the reaction conditions, including the input voltage (2.1-3.8 kV), the initial pH value (3.1-10.3), the center dot OH inhibitors, the inorganic ions, and the natural organic matter (NOM), on the OTC degradation efficiency were measured, and the optimal parameters were determined based on the results of single factor experiments. The results showed that the OTC removal efficiency and the kinetic constant can be increased by enhancing the input voltage, and about 93.7% of the OTC was removed at 3.8 kV and in a neutral pH (6.9) solution. The presence of center dot OH inhibitors, inorganic ions and NOM in the solution can reduce the OTC removal efficiency and the kinetic constant. Moreover, compared to dry O2 strong ionization dielectric DBD, the active particle yield (center dot OH, O3, H2O2), the kinetic constant, and the TOC removal by humid O2 strong ionization discharge DBD were better. Subsequently, five main by-products were identified and four different transformation pathways, including hydroxylation (+16 Da), deamidation (-46 Da), demethylation (-14 Da), and dehydration (-18 Da), were observed. In addition, the acute toxicity of the intermediates was reduced, but the mutagenicity of the biotoxicity was positive.