Enhanced generation of active oxygen species induced by O₃ fine bubble formation and its application to organic...

By using O₃ fine bubbles that promote the mass transfer of O₃ to the liquid phase and the conversion of the dissolved O₃ into active oxygen species with a high oxidation potential, an improved liquid-phase oxidation technique was developed to accelerate the degradation of an organic compound at a constant O₃ flow rate. By the use of a dielectric-barrier-discharge reactor, O₂ was converted into O₃ at an O₂ flow rate of 0.56 mmol/(L·min), with 5 mol% O₂-to-O₃ conversion. Using a self-supporting bubble generator, O₃ bubbles with an average diameter (d_bbl) of 50 µm were continuously supplied into a solution in TBA (OH• scavenger) at 303 K, and the TBA being degraded. For comparison, O₃ bubbles with d_bbl values of 200-5000 µm were obtained using a dispersing-type generator. It was found that the minimization of bubble diameter accelerated both O₃ dissolution, as a consequence of the increase in the gas-liquid interfacial area and the residence time of the bubbles, and enhanced OH• generation, because of the increase in contact probability between dissolved O₃ and OH^- at the minute gas-liquid interfaces, caused by the accumulation of OH^- around the fine bubble surfaces. To ascertain the influence on organic compound degradation of the improved oxidation potential, bisphenol A, as a model compound, was degraded by O₃ bubble injection at different d_bbl values. Sequentially, the high OH• selectivity obtained by minimizing the bubble diameter can effectively achieve the rapid degradation of organic compounds and intermediates under a constant O₃ flow rate.