Influence of micron-sized air bubbles on sonochemical reactions in aqueous solutions exposed to combined ultrasonic irradiation and aeration processes

Sonochemical reactors are promising for wastewater treatment applications. However, the combination of ul-trasonic irradiation and aeration processes raises questions regarding the extent to which entrained air bubbles influence sonochemistry. In this study, the effect of micron-sized air bubbles (20 and 70 mu m, 0.1-5.0 vol%) on sonochemical activity, based on KI dosimetry, was tested in a horn-type reactor (20 kHz). Bubbles were generated using the pressurization-depressurization method. The results showed that low bubble concentrations increased sonochemical yields but higher concentrations tended to decrease the yields. Compared with the bubble-free case, 20-mu m bubbles enhanced sonochemistry at all concentrations, while 70-mu m bubbles inhibited sonochemistry at the highest concentration (5.0 vol%). Two regimes, acoustic attenuation and nucleus intro-duction, were identified as inhibiting and enhancing sonochemical effects, respectively, and their dependence on bubble characteristics was examined. These results are significant as investigation into these regimes will allow deeper understanding of the key factors controlling sonochemistry in the presence of micron-sized air bubbles and could be used to design sonoreactors equipped with aerators.