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

Abstract

• A large volume strong ionization DBD system was applied to the OTC removal. • Combination of H 2 O and O 2 with Venturi jet had a positive effect on the removal. • The higher formation of OH, O 3 , H 2 O 2 was favorable for the OTC degradation. • Compared with dry O 2 DBD, the active particle yield could be improved. • Possible degradation pathways of the OTC and the toxicity analysis were proposed. In this study, the degradation of oxytetracycline (OTC) in aqueous solution by humid O 2 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 O 3 and H 2 O 2 concentrations, the existence of high concentrations of hydroxyl radicals ( OH) (0.85 mmol/L), O 3 (14.2 mg/L), and H 2 O 2 (63.3 mg/L) produced via humid O 2 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 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 OH inhibitors, inorganic ions and NOM in the solution can reduce the OTC removal efficiency and the kinetic constant. Moreover, compared to dry O 2 strong ionization dielectric DBD, the active particle yield ( OH, O 3 , H 2 O 2 ), the kinetic constant, and the TOC removal by humid O 2 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.