Decoloring of Aqueous Solutions of Indigocarmine Dye in An Acid Medium by H 2 O 2 /UV Advanced Oxidation

This study reports on the advanced oxidation of indigocarmine dye—5,5′-indigodisulphonate disodium (5,5′-IDS)—in an acid medium by means of the combined action of polychromatic UV-radiation and H₂O₂. The influence of different parameters, such as UV-radiation dose, hydrogen peroxide concentration, temperature, and pH in the rate equation of this photo-oxidative process has been studied. The experiments were carried out utilizing a polychromatic UV high-pressure mercury lamp to irradiate highly colored aqueous solutions of indigocarmine. The kinetic experiments showed a linear dependence between the rate constant, the UV-radiation dose, and the H₂O₂ concentration, whereas pH and T does not significantly affect the decoloring rate. A feasible reaction scheme is proposed, from which the rate of the global process is deduced. This equation rate is in agreement with the observed variations of the experimental rate constant when modifying the different kinetical factors. The results showed that highly colored aqueous solutions of indigocarmine (9 × 10⁻⁵ mol L⁻¹) can be effectively decolorized in an acid medium, in a short time interval (10 min) at room temperature by applying a UV-radiation dose of 29.21 W L⁻¹ and low H₂O₂ concentration (10⁻³ mol L⁻¹). The effluent of the treatment was colorless and nontoxic, according to the Microtox^® tests routine analyses. Thus, H₂O₂/UV advanced oxidation of indigocarmine may be an efficient alternative treatment for decolorizing textile wastewater containing this dye, in the referred experimental range of conditions.