Degradation of Low Concentration Methyl Orange in Aqueous Solution through Sonophotocatalysis with Simultaneous Recovery of Photocatalyst by Ceramic Membrane Microfiltration

Photocatalysis is a promising technology for wastewater treatment, particularly for mineralization of nonbiodegradable and toxic components in wastewater. TiO2 is usually utilized as photocatalyst in slurry reactors in order to overcome mass transfer limitations. The difficulty in recovering TiO2 photocatalyst from treated water hindered its wide application. In this work, a novel process efficiently integrating sonophotocatalysis for methyl orange degradation and ultrasonic-enhanced ceramic membrane microfiltration for TiO2 separation was proposed and demonstrated. The results indicated that ultrasonic introduction could enhance photocatalysis reaction rate through cavitation effect, a synergetic effect between sonolysis and photocatalysis was found, and that is closely related with working conditions. Ceramic membrane microfiltration could efficiently recover TiO2 photocatalyst with a mean granular size of 0.33 μm from slurry reactor, achieving 99.9% recovery rate. Ultrasonic introduction into microfiltration process efficiently increased transmembrane permeation flux, suppressing membrane fouling under optimal working conditions. However, due to the problems associated with conversion efficiency of ultrasonic energy and the uncertain synergistic effect of sonolysis and photocatalysis, there is still much work before application of this process for wastewater treatment.