Highly synergetic effect for norfloxacin degradation by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system

Abstract

• Coupling plasma with Fe (III)–S (IV) system can efficiently remediate NOR and prolong it during plasma-off. • Underwater bubble plasma accelerates radical chain reactions and improves the transfer efficiency. • Enhanced NOR degradation is attributed to the presence of • OH and SO 4 •− . • • OH and SO 4 •− can be regenerated by chain reactions through plasma-generated effects. • The synergetic degradation mechanism and possible contribution of approaches are proposed. Antibiotics are widely used to treat or prevent infectious diseases in human and veterinary medicine. Excessive residues in the aquatic environment lead to increasingly prominent antibiotic pollution; therefore, it is urgent to develop sustainable strategies for rapidly degrading antibiotics. In this study, a highly synergetic effect for norfloxacin (NOR) remediation is achieved by coupling underwater bubble plasma formation with a Fe (III)–S (IV) system due to the efficient utilization of reactive species in chain reactions. The degradation rate using synergetic approach can reach 76.4% within 50 min discharge, and further increases significantly to 94.4% after 5 h post-discharge. The effects of pulsed peak voltage and Fe (III)/S (IV) dosage on NOR removal are characterized. The existence of hydroxyl radicals ( • OH) and sulfate radicals (SO 4 •− ) are proved by electron spin resonance spectrometer (ESR) during degradation. Furthermore, radical scavenger experiments demonstrate that • OH and SO 4 •− play a crucial role in degradation. Underwater bubble plasma provides the oxic and acidic liquid environment for the Fe (III)–S (IV) system to accelerate the self-perpetuating chain reactions. These reactions not only introduce SO 4 •− and generate more • OH during plasma-on, but also induce their regeneration and further prolong the degradation process during plasma-off through plasma-generated effects. Finally, the degradation intermediates of NOR are identified, and a possible degradation pathway is proposed. The possible contribution weight of each approach on the degradation rate is speculated. These new findings offer promising applications for developing a technology with real potential for the treatment of organic compounds in industrial wastewater treatment.