Ultrasonically activated peroxymonosulfate oxidation for advanced water treatment: Cavitation mechanism, free radical generation and process simulation

The persistent presence of recalcitrant organic pollutants in aquatic environments highlights the urgent need for efficient and sustainable water treatment technologies. This study investigated the application of the ultrasonically activated peroxymonosulfate system for organic pollutant degradation, with a focus on elucidating its cavitation mechanism, radical generation, and multiphysics characteristics. Experimental results demonstrated that the US-PMS system is pH-tolerant, achieving 92.4% removal of the model pollutant (methylene blue) within 60 min under optimal reaction conditions, with a reaction stoichiometric efficiency of 41.7%. Radical quenching experiments and EPR confirmed that ·OH and SO₄^·- are the dominant radical species in the reaction. Based on the Keller-Miksis single-bubble model, the physical property changes during cavitation bubble collapse and their influence on radical activation were quantitatively analyzed, revealing the intrinsic link between ultrasonic cavitation and radical generation. Furthermore, COMSOL Multiphysics simulations identified a "bottom activation-top mixing" functional zone within the reactor. This zoning enhances mass transfer and PMS activation efficiency through the synergistic coupling of acoustic, flow, and thermal fields. These findings provide novel insights and theoretical foundations for optimising the US-PMS system and facilitating its scale-up application in industrial wastewater treatment.