Remediation of ciprofloxacin-contaminated soil by nanosecond pulsed dielectric barrier discharge plasma: Influencing factors and degradation mechanisms

Abstract

Abstract The continuous release of antibiotics in soil environment poses a serious threat for soil and water quality and consequently human health. However, research efforts focused on the effective remediation of antibiotic-polluted soil are still very limited. In this study, a nanosecond pulsed dielectric barrier discharge (nsp-DBD) plasma system was used for the first time to remediate soil contaminated by ciprofloxacin which is one of the most widely used, persistent and genotoxic antibiotics. Various cold atmospheric plasma (CAP) operating parameters were investigated and optimized. The optimal moisture content and air flow rate were determined at 5% and 1.0 L min−1, respectively. Ciprofloxacin degradation increased with pulse voltage and pulse repetition rate and decreased with higher initial concentrations in the soil. At optimal conditions (pulse voltage 17.4 kV, pulse frequency 200 Hz), ciprofloxacin was completely degraded (~99%) in soil, at very short nsp-DBD treatment time (~3 min), with the corresponding energy efficiency being 4.6 mg/kJ. The relative distribution and identity of major ciprofloxacin degradants generated was determined by UPLC-MS analysis. This led to the generation of a degradation map that is consistent with hydroxyl radical-driven successive hydrogen atom abstractions and hydroxyl radical recombination events at the onset of the process followed by singlet oxygen mediated degradation. Interestingly, the degradation pattern observed under nsp-DBD conditions shares several aspects with the in-vivo metabolic profile of ciprofloxacin.