Degradation of antibiotic enrofloxacin in water by gas-liquid nsp-DBD plasma: Parametric analysis, effect of H2O2 and CaO2 additives and exploration of degradation mechanisms

Enrofloxacin (ENRO) is a highly toxic fluoroquinolone antibiotic widely used in a broad spectrum of human activities and therefore increased ENRO levels found in aquatic environments pose serious threats for human and livestock health. In this study, a gas-liquid nanosecond pulsed dielectric barrier discharge (nsp-DBD) plasma reactor was used for the degradation of ENRO in aqueous solutions. The increase of pulse peak voltage and the pulse repetition rate, up to a certain limit, were found to enhance ENRO degradation efficiency, degradation rate and energy yield. Under the optimum pulse voltage and pulse frequency, ENRO was completely degraded after 20 min with the corresponding energy yield being 1.1 g/kWh. Air and O-2 as working gases displayed superior impact on degradation compared to N-2. Additives such as CaO2 and H2O2 were found to enhance the degradation rate with CaO2 being superior promoter compared to H2O2. The UV-Vis emission spectra of the plasma discharge revealed the generation of various reactive nitrogen and oxygen species in the gas phase whereas the concentrations of the reactive gaseous NOx were also measured. In liquid phase, the importance of center dot OH and O-1(2) in the degradation process was confirmed by using appropriate scavengers, while H2O2 concentration was quantified by reflectance photometry. A degradation pathway was proposed following HPLC and UPLC/MS analysis of treated samples at various time points of the nsp-DBD treatment. Overall, the complete degradation of enrofloxacin in water was achieved with very high-energy yield suggesting that the current nsp-DBD system could be considered an appealing alternative as a cost-effective technology for the remediation of antibiotic-polluted water systems.