Degradation of CIP by circulating water-electrode DBD plasma: Degradation performance, key reactive species, and pathway analysis

Abstract

In this work, a novel circulating water-electrode DBD device with double aeration is designed for ciprofloxacin (CIP) removal, focusing on its degradation performance, the degradation pathways, and the role of reactive species involved in the process. The results show that this system exhibits a high Energy Yield (EY) of up to 121 g kWh⁻¹ with 98.2 % degradation efficiency of CIP, much superior to its counterparts. It due to that the energy consumption is greatly reduced by circulating water cooling, pulse modulation, and double aeration. In this DBD device, the role of ($e^{-}$$e^{-}$) is weak, and the typical Reactive oxygen species (ROSs) (¹O₂, $\bullet {\mathrm{O}}_2^{-},\mathrm{a}\mathrm{n}\mathrm{d}\bullet \mathrm{O}\mathrm{H}$$\bullet {\mathrm{O}}_2^{-},\mathrm{a}\mathrm{n}\mathrm{d}\bullet \mathrm{O}\mathrm{H}$) play an important role in the CIP degradation performance, following the order of contribution: ¹O₂ > $\bullet {\mathrm{O}}_2^{-}$$\bullet {\mathrm{O}}_2^{-}$> $\bullet \mathrm{O}\mathrm{H}$$\bullet \mathrm{O}\mathrm{H}$, which is verified by the quenching experiment. CombinOed with intermediate product analysis from liquid chromatography-mass spectrometry (LC-MS) and Density Functional Theory (DFT) simulation, two potential degradation pathways are proposed: One involving attack on the quinolone ring and the other on the piperazine ring. Besides, the role of reactive species in the degradation process is also inferred. Additionally, the toxicity of the intermediates is assessed. This work is expected to provide an efficient and energy‐saving plasma technique for antibiotic wastewater.