Comparison of hydrogen peroxide-based processes for treating dye-containing wastewater: Decolorization and destruction of Orange II azo dye in dilute solution

This work was performed to compare several Advanced Oxidation Processes in the treatment of wastewater containing an organic dye. In particular, aqueous solutions containing 50 ppm Orange II (OG-II) in 0.05 M Na2SO4 at pH 3 and at room temperature were subjected to three different hydrogen peroxide-based oxidation processes in a recycle-batch reactor: Direct Photolysis, the Electro-Fenton process, and a Photoelectro-Fenton process with two different iron(II) concentrations (0.2 mM and 0.5 mM). By producing OH radicals as an active oxidant, all of these processes remove the color from the solution in a short time, but the Photoelectro-Fenton with the lower iron level performed best. It not only decolorized the solution in less than 5 min, but it also destroyed 80% of TOC in 60 min of treatment. The comparable TOC removal efficiency was 63% for the Electro-Fenton system and only 31% for Direct Photolysis. It was found that higher levels of catalytic iron ions are detrimental to the Fenton-based processes.