Effects of hydrogen peroxide in a fluidized bed photocatalytic reactor for wastewater purification

There have been a number of studies indicating that hydrogen peroxide can enhance photocatalytic oxidation of organics by TiO2, which is known to have relatively low quantum yield. There are also studies that reported negative effect of adding hydrogen peroxide to a photocatalytic system. In this study, various combinations of TiO2 and hydrogen peroxide were investigated in a fluidized bed reactor in order to analyze the effect of their combined use versus single applications. A new composite photocatalyst that integrates titanium dioxide with an adsorbent zeolite supported on glass beads was implemented for the use in the photoreactor. Phenol was used as a model contaminant and 254 nm UV lamps were used for irradiation. Overall, the outcome of the experiments pointed to the advantageous use of the combination of photocatalysis with hydrogen peroxide over their individual use. Moreover, it was found that photocatalytic oxidation of phenol can be promoted with relatively small amounts of H2O2 (no more than one-fifth of what would be required stoichiometrically). When all reasonable combinations were explored, it was found that the outcome depended on the ratio between H2O2 and titania loading. The series with lower H2O2 and higher catalyst loading showed synergetic behavior for the process of phenol degradation but the rate of degradation decreased with further addition of H2O2. In the other series with higher H2O2 and lower catalyst loading, phenol degradation was found to continuously increase with the increase of H2O2. The combination of the lowest catalyst loading (0.21 g/l) with 20% H2O2 showed superior performance for phenol degradation in this reactor. Results of this study open new research window for a more complex approach to photocatalytic experiments where photocatalysis can be combined with hydrogen peroxide. (c) 2006 Elsevier B.V. All rights reserved.