Solar photocatalytic degradation of dichloroacetic acid with silica-supported titania at pilot-plant scale

A multivariate analysis using experimental design techniques was performed to determine the effect of iron, hydrogen peroxide and titanium dioxide in the solar photodegradation of dichloroacetic acid in a combined TiO2/photo-Fenton process. The study was carried out at pilot-plant scale, using TiO2 supported on silica as the heterogeneous photocatalyst to facilitate separation of the solids after the reaction, and iron concentrations of less than 3 mg L−1 to avoid removal of iron from the effluent. The results show that iron is the most important factor influencing the reaction rate, which suggests that in strongly acidic solutions, the Fenton mechanism controls the process even at such low iron concentrations. Under these conditions, the expected synergism between TiO2 and iron degradation pathways seems to be negligible compared to the antagonistic effect between hydrogen peroxide and TiO2, which reduces the activity of the combined system. However, in the absence of hydrogen peroxide, the activity achieved by the combined Fe/TiO2 system is similar to that of the photo-Fenton process, with the advantage that H2O2 is replaced by a reusable TiO2-based catalytic material. Consequently, the analysis of pilot-plant operation economics took not only the degradation rate, but also the cost of chemicals into account.