Experimental and numerical investigation on the effect of frequency combinations on PFOA defluorination by dual-frequency ultrasound coupling persulfate

Abstract

Due to the synergistic contribution, dual-frequency ultrasound can significantly enhance the degradation of organic contaminants, but the effects of different frequency combinations have not been clarified and need to be explored. In this study, several frequency combinations were designed firstly both in experimental exploration and numerical simulation within the dual-frequency ultrasound coupling persulfate (PS) system to investigate the effect of frequency combinations on the degradation of perfluorooctanoic acid (PFOA). The monitoring parameters included the defluorination percentage and the simulated maximum expansion ratio (Rmax/R0). The simulated maximum expansion ratios in different frequency combinations showed a high correlation with their defluorination results, indicating that the discrepancy in defluorination effects of different frequency combinations was mostly attributed to their various maximum expansion ratios. Additionally, various maximum expansion ratios could result in different maximum solution temperatures, and the increase in temperature was found positive for PFOA defluorination in this study. In addition, the synergistic parameters that affected the maximum expansion ratio were analyzed, including the phase difference, frequency ratio, and frequency value. The obtained results showed that the maximum expansion ratio varied with different phase differences, and the frequency ratio could affect the variation trend. For the same fundamental frequency, the larger the frequency ratio, the smaller the maximum expansion ratio. Under the same phase difference and frequency ratio, the larger the frequency value, the lower the cavitation.