Intensification of ozone mass transfer and hydroxyl radical generation in HC-UC/RF coupled system: Promotion and application

Abstract

Advanced oxidation processes (AOPs) are widely used in water treatment, yet traditional ozone (O₃)-based processes are limited by O₃'s low water solubility and mass transfer efficiency. This study established a coupled system that integrates hydrodynamic cavitation (HC), ultrasonic cavitation (UC), and rotational flow field (RF) to enhance ozonation. Considering O₃ decomposition, this study investigated the effects of various operating factors on the mass transfer coefficients and generation of hydroxyl radicals (^•OH). The results showed that the HC-UC/RF system overcame the limitations of the individual technologies. HC enhanced turbulence and generated microbubbles, improving the contact efficiency between O₃ and the liquid phase. Meanwhile, the synergistic effect of rotational flow and UC optimized the distribution of cavitation bubbles within the reactor, thereby enhancing the cavitation effect. This coupled system significantly increased the generation of ^•OH and mass transfer efficiency of O₃. Under the optimal conditions of 43.92 mg/L O₃ concentration, 100 L/h O₃ gas flow rate, 20 kHz ultrasonic frequency, and 600 W ultrasonic power, the yield of ^•OH was 0.2717 μmol/(L min), the decomposition rate constant of O₃ was 0.5457 min⁻¹, and the volumetric mass transfer coefficient was 0.1166 min⁻¹. The degradation of tetracycline and norfloxacin was compared across different systems, further verifying the enhanced oxidizing capacity of the coupled system. Specifically, the HC-UC/RF system achieved rapid antibiotic degradation, with a 57 % TOC removal efficiency after 16 min. This study presents a novel hybrid system that offers additional insights into enhancing the efficiency of O₃-based AOPs.