Total mineralization of mixtures of Tartrazine, Ponceau SS and Direct Blue 71 azo dyes by solar photoelectro-Fenton in pre-pilot plant.

Mixtures of monoazo Tartrazine, diazo Ponceau SS and triazo Direct Blue 71 dyes with 105 mg L of total organic carbon (TOC) in 0.050 M NaSO at pH 3.0 have been treated by solar photoelectro-Fenton (SPEF). Experiments were carried out in a 2.5 L pre-pilot plant with a Pt/air-diffusion cell coupled to a solar planar photoreactor. Comparative trials were made by anodic oxidation with electrogenerated HO (AO-HO) and electro-Fenton (EF) to better understand the role of oxidizing agents. AO-HO gave poor degradation due to the low oxidation ability of OH formed at the Pt anode and HO produced at the cathode. Similar color removal was achieved in EF and SPEF because the main oxidant was OH formed in the bulk from Fenton's reaction. EF yielded partial mineralization by formation of molecules with high stability against OH. In contrast, these by-products were rapidly photolyzed under sunlight irradiation in SPEF, which was the most powerful treatment. Up to 8 linear final carboxylic acids were detected, along with the release of sulfate and ammonium ions. The effect of Fe and azo dye concentrations, and current density over the SPEF performance was assessed. Total mineralization of azo dyes mixtures occurred when operating up to 105 mg L TOC with 0.50 mM Fe at 100 mA cm.