Exploring the impact of ultrasound on antibiotic-resistant bacteria inactivation in the sulfidated zero valent iron/persulfate system

Abstract

Antibiotic resistance poses huge challenge on human beings. In this study, we evaluated the removal of antibiotic-resistant E. coli and antibiotic-resistant genes through sulfidated zero valent iron activated persulfate system under ultrasound (33 kHz, 40 W). In the proposed system, the inactivation efficiency was significantly improved, 7.8 log AR E. coli were inactivated in 30 min. And antibiotic-resistant genes (ampC and TetB) were also removed after treatment by the system. Impressively, a switch in the AR E. coli decay model from pseudo second order kinetics (R2 = 0.969) to first order kinetics (R2 = 0.981) was found with the introduction of ultrasound. Ultrasound changes in cellular and S-ZVI/PDS reaction processes are the main reason. Ultrasound converted the system from a heterogeneous process to a homogeneous process. Fe2+ played the main role in the radical generation and the fate of Fe2+ was explored by XPS and XRD. Not only sulfidation promoted the release and regeneration of Fe2+, but also ultrasound accelerated the migration of Fe2+ from the S-ZVI surface to the solution. Reactive oxygen species (OH·, SO4-·, and O2-·) were the vital reasons for antibiotic-resistant E. coli elimination. TEM and FTIR analyses illustrated the changes in cell structure and substance after treatment. Ultrasound boosted cell membrane deformation and rupture which accelerated their inactivation under free radical attack.