Removal of antibiotic resistant bacteria and genes by nanoscale zero-valent iron activated persulfate: Implication for the contribution of pH decrease

The mechanism of removing antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) by persulfate was attributed to the generation of reactive oxygen species (ROS). However, the potential contribution of decreased pH in persulfate system to ARB and ARGs removal has rarely been reported. Here, the efficiency and mechanism of removing ARB and ARGs by nanoscale zero-valent iron activated persulfate (nZVI/PS) were investigated. Results showed that the ARB (2 x 10(8) CFU/mL) could be completely inactivated within 5 min, and the removal efficiencies of sul1 and intI1 were 98.95% and 99.64% by nZVI/20 mM PS, respectively. Investigation of mechanism revealed that hydroxyl radicals was the dominant ROS of nZVI/PS in removing ARB and ARGs. Importantly, the pH of nZVI/PS system was greatly decreased, even to 2.9 in nZVI/20 mM PS system. Impressively, when the pH of the bacterial suspension was adjusted to 2.9, the removal efficiency of ARB, sul1 and intI1 were 60.33%, 73.76% and 71.51% within 30 min, respectively. Further excitation-emission-matrix analysis confirmed that decreased pH contributed to ARB damage. The above results on the effect of pH indicated that the decreased pH of nZVI/PS system also made an important contribution for the removal of ARB and ARGs.