Photocatalytic Degradation of Azo Dyes. Pilot Plant Investigation

The UVB-induced photocatalytic degradation of Methyl Red and Methyl Orange (azo dyes used in the textile industry) containing solutions was carried out by the use of a laboratory-scale pilot plant where the catalyst, TiO2 (anatase), was immobilized at the bottom of a channel through which the liquid was recirculated under UVB irradiation. The plant was preliminarily characterized hydrodynamically, i.e., flow-rate, hydraulic gradients, and residence time. Photodegradation kinetics were followed by UV–vis absorption measurements of the residual dye concentration in the liquid-phase, and the synergistic effects of the catalyst and radiation in promoting the abatement of dyes was demonstrated in the concentration range 0.3–5.0 mg/L. Kinetic data were correlated by the use of first-order (or pseudo-first-order) models up to the concentration range 0.7 mg/L; at higher concentrations, zero-order models (pure catalytic control) better correlated the experimental data. Photocatalytic degradation of Methyl Red was ...