Degradation of tetracycline hydrochloride by nanosecond-pulsed plasma bubbles: effects of gas composition and discharge mode

Extensive quantities of antibiotics have been released into surface and groundwater systems through various sources such as aquaculture, medical, and chemical wastewater. This has led to the spread of antibiotic resistance genes, resulting in multidrug resistance in pathogenic bacteria and posing risks of chronic toxicity, mutagenicity, carcinogenicity, and teratogenicity. Therefore, efficient degradation methods for antibiotics in wastewater are essential to protect human health and ecological safety. Among current wastewater treatment technologies, non-thermal plasma technology has gained significant attention due to its low cost, ease of operation, and lack of secondary pollution. However, challenges such as low energy efficiency and inadequate utilization of key liquid-phase reactive species persist. In this study, a highly efficient plasma bubble reactor equipped with a nanosecond pulsed power supply was employed to degrade tetracycline hydrochloride (TCH) wastewater. Under the same discharge power, two discharge modes (spark discharge and dielectric barrier discharge (DBD)) were investigated with the introduction of different gases (air, argon, nitrogen). The results indicate that the DBD air mode exhibited the highest degradation efficiency (90.8% degradation in 10 min), with the highest energy yield (3.39 g kWh⁻¹). Further investigation into the optimal DBD air mode was conducted to evaluate the effects of gas flow rate, discharge voltage, discharge frequency, and solution properties on the degradation of TCH. Optimization studies revealed that TCH degradation was maximized at a gas flow rate of 1000 sccm, 12 kV discharge voltage, and 5 kHz frequency (specific to the experimental setup used in this study). Key active particles involved in the degradation mechanism were analyzed through scavenger experiments, indicating that superoxide radical (·O₂⁻) plays a critical role in TCH degradation. Preliminary biocompatibility tests using mung bean germination suggest the feasibility of discharging treated water back into the environment.