Enhanced physicochemical properties of micro-nano bubbles water via high-speed vortex synergistic ultrasound and mechanisms of sterilization and pesticide degradation

This study developed a novel high-speed vortex synergistic ultrasound method to enhance the physicochemical properties of air micro-nano bubble (MNB) water by increasing micro-nano bubble concentration. Using response surface methodology with ultrasonic power, treatment time, and airflow rate as variables, optimal conditions were established at 9 min treatment time, 150 W ultrasonic power, and 90 mL/min airflow rate. The resulting MNB water exhibited improved characteristics, including increased dissolved oxygen concentration (11.35 mg/L), decreased pH (6.37), and significantly reduced bubble size (350 nm), along with enhanced stability during 48 h of storage compared to preparations using a single method (p < 0.05). Mechanistic analysis identified three key pathways driving increased oxidative capacity: (1) size-dependent effects of nanobubbles enhancing gas-liquid interface reactions; (2) increased hydrogen ion concentration from dissolved carbon dioxide and the generation of nitrous and nitric acids via cavitation-induced nitrogen fixation; and (3) potential generation of oxidative species via ultrasonic cavitation-vortex coupling. These mechanisms resulted in efficient pesticide degradation, achieving 16.22% removal of clothianidin and 33.00% of imidacloprid, alongside with strong bactericidal effects of 2.17-log reduction for Escherichia coli and 5.80-log reduction for Staphylococcus aureus . The established relationship between bubble properties and contaminant removal efficiency offers a theoretical basis for applications of MNB water technology.