Synergistic Enhancement in Hydrodynamic Cavitation combined with Peroxymonosulfate Fenton-like Process for BPA Degradation: New Insights into the Role of Cavitation Bubbles in Regulation Reaction Pathway

The combination of hydrodynamic cavitation (HC) and Fenton-like oxidation technology can dramatically enhance the pollutant removal capacity, however, the synergistic effect of cavitation and catalyst on reactive oxygen species (ROS) generation remained enigmatic. In this study, we established a combined system based on HC and Ce-MnFe₂O₄ activated peroxymonosulfate (PMS) for BPA removal, and attentions were paid on the role of cavitation bubbles. Study results show that the combination of HC in Ce-MnFe₂O₄ activated PMS could mediate the degradation of BPA from the non-radical pathway dominated by ¹O₂ to •O₂⁻ dominated radical pathway. Both controlled experiments and theoretical calculations revealed that the cavitation bubbles with different sizes play the dominant role in ROS generation. The microjets produced by the collapse of cavitation bubbles could create a large number of oxygen vacancy defects on Ce-MnFe₂O₄ surface, which modify the activation barrier of PMS and facilitate the generation of •O₂⁻ thermodynamically. The stable existing cavitation bubbles with the size of 100∼400 nm could create considerable gas-liquid interface. The molecular dynamics simulations show that the nano bubbles can concentrate the BPA and increase the probability of contacts between BPA and Ce-MnFe₂O₄, hence effectively solve the issues of short lifetime of •O₂⁻ radicals and limited mass transfer distance to strengthen the reaction. In addition, the PMS/Ce-MnFe₂O₄/HC system not only achieves the satisfied COD (95%) and TOC (65%) removal efficiency but also enabled the BPA-contaminated water with a low energy cost of 0.065 kWh·m⁻³ and oxidant cost, highlighting the application potential of the HC technology for contaminated water.