Photochemical vs. photocatalytic azo-dye removal in a pilot free-surface reactor: Is the catalyst effective?

Advanced oxidation processes (AOPs) are potential alternatives for treatment of effluents containing hardly biodegradable textile dyes. These processes imply the generation and subsequent reaction of hydroxyl radicals (OH[rad]), which are some of the most powerful oxidizing species. Among AOPs, ozonation (often combined with H2O2, UV, or both), showed to be promising either for the complete mineralization of dyes or for their transformation into less complex and more easily biodegradable structures. In this study, the photocatalytic degradation of Levafix Brilliant Red E-6BA reactive textile dye has been investigated in presence of H2O2 by means of a Free-Surface Reactor (FSR), with two types of Hg lamps (Medium Pressure, MP, and Low Pressure, LP) irradiating the liquid from the top of the reactor without direct contact with the liquid. The dye degradation efficiency of the process has been evaluated by comparing the reaction rate constants (RRC) from experimental data and the total power consumption for wastewater treatment (RWW). In order to increase the photodegradation efficiency, several TiO2 based photocatalysts (TiO2 commercial or prepared by Flame Spray Pyrolysis (FSP), bare or loaded with 0.1 mol% Pd or Au) have been added to the batch system. The results suggest that the MP UV-FSR requires less energy for dye removal in case of high dye concentration, whereas, for lower dye concentration, LP UV-FSR shows better performance in terms of energy consumption. Bare P25 even in relatively low quantity (100 mg/dm3) showed to be an active co-adjuvant for dye decoloration and aromatic structures degradation with half the energy consumption than a solution without photocatalyst.