Degradation effect and mechanism of gas-liquid phase dielectric barrier discharge on norfloxacin combined with H2O2 or Fe2+

Abstract

Norfloxacin (NOR) is a typical kind of Fluoroquinolone antibiotics which is extensively used around the world. Residues of NOR have been found continuously increasing in the water systems thus posing detrimental effects to the aquatic ecosystem and human health. In this study, the degradation effect and mechanism on NOR in aqueous solution are investigated by gas-liquid phase dielectric barrier discharge (DBD) plasma combined with different catalysts (H2O2 or Fe2+). The concentrations of three representative plasma-generated long-lived reactive species (H2O2, O3 and NO3-) were measured in dH2O and found enhancing with the lengthening discharge period. Variations on the treatment parameters were carried out in discharge power, initial solution pH and the concentration of catalysts. A discharge power at 60 W provided optimal balance on the degradation effect and energy efficiency would be beneficial, while there is not much impact from the initial solution pH on NOR degradation. Both H2O2 and Fe2+ at low concentration (0.5–10 mg/L of Fe2+, 0.1–1.0 mmol/L of H2O2) were observed contributing to the improvement on the NOR degradation rate, while inhibition would occur at high concentration (10–20 mg/L of Fe2+, 1.0–2.0 mmol/L of H2O2). The DBD/H2O2 (0.5 mmol/L)/Fe2+ (10 mg/L) system was found the optimal condition to achieve a high NOR degradation rate of more than 98% after plasma treatment for only 0.5 min at discharge power of 60 W. Moreover, 72.3 ± 1.7% of the total organic carbon (TOC) in NOR solution have been removed in the DBD/Fe2+ (10 mg/L) system at 15 min which signifies a high mineralization efficiency. The cleavage of piperazine ring and quinolone ring, defluorination and hydroxylation are considered the major pathways for NOR degradation. The biological toxicity of the plasma/Fe2+-induced degradation intermediates has been detected and it fluctuated with the treatment time and finally declined. Therefore, the DBD/catalyst system could be an effective and promising method on pharmaceutical wastewater treatment in the future.