Synergistic degradation of venlafaxine by ultrasound/persulfate process: governing factors, mechanism and DBPs formation

Ultrasound (US) coupled with persulfate (PS) forms an efficient AOP for degrading emerging contaminants. However, information on the key factors governing the US/PS synergy and underlying mechanism is still limited. In this study, venlafaxine (VEN) was selected as the model compound to systematically examine the effects of key parameters (e.g., ultrasonic frequency, power, PS dosage, and initial pH) as well as the water matrix on the synergy of the US/PS process. Additionally, compounds with varying physicochemical properties were chosen to elucidate their roles in this synergy. The results showed that elevated ultrasonic frequency and power accelerated VEN degradation but they diminished the process synergy. In contrast, a higher PS dosage and acidic conditions enhanced the synergy. Although anions and humic acid exerted little influence on US alone, they inhibited the US/PS process to varying degrees, thus reducing its synergy. Notably, log K OW was a key factor influencing the US degradation rate and US/PS synergy. Furthermore, SO 4 ●– reactivity was found to moderately influence the synergy. To elucidate VEN degradation mechanisms, LC/TOF/MS and DFT calculations identified transformation intermediates and pathways, while COMSOL simulations characterized ultrasonic reactor hydrodynamics (pressure, temperature, and velocity fields) under varying power levels. Although a few products identified via ECOSAR prediction exhibited higher toxicity, the overall toxicity could be reduced by prolonging the US/PS treatment time. Finally, a preliminary experiment was conducted to investigate the influence of US/PS pretreatment on the formation potential of DBPs. US/PS pretreatment promoted the formation of trichloronitromethane during post-chlorination, whereas alternative disinfectants (NH 2 Cl and ClO 2 ) were effective at suppressing it. This study deepens the mechanistic understanding of the key factors that govern the effectiveness of the US/PS process for micropollutant remediation in water.