Process intensification of the ozone-liquid mass transfer in ultrasonic cavitation-rotational flow interaction...

A study on the intensification of ozone mass transfer in rotational flow field and UC-RF coupled-field was conducted. Two important operational parameters namely liquid flow rate and ultrasonic power, were optimized with regard to the ozone mass transfer efficiency. Results showed that the mass transfer coefficient (K_La) increased with liquid flow rate (up to 14 L min^-1) and ultrasonic power (up to 1000 W). The maximum K_La value (1.0258 min^-1) was obtained with the UC-RF coupled-field. Moreover, the reinforcement of mass transfer efficiency was promoted by the rotational flow field and UC-RF coupled-field due to the increase in the ozone-liquid contact area, intensification of turbulence, acceleration of interface renewal, and extension of residence time. Ozone microbubbles rose in the reactor in a spiral manner. In addition, the microbubbles produced in the rotational flow field served as cavitation nucleus that helped to generate the cavitation effect. The effective degradation of di-butyl phthalate (DBP) confirmed that its removal was improved by the ozone-liquid mass transfer and the promotion of hydroxyl radicals (·OH) production. The synergistic effect of DBP degradation via ultrasound-enhanced ozonation was significant.