Electrochemical degradation of RB-5 dye by anodic oxidation, electro-Fenton and by combining anodic oxidation-electro-Fenton in a filter-press flow cell

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract This paper reports the removal of a recalcitrant and toxic dye, Reactive Black 5 (RB-5) by three methods; 1) anodic oxidation (AO) on Boron-Doped Diamond (BDD), 2) by electro-Fenton (EF) process where hydrogen peroxide was produced by oxygen reduction on reticulated vitreous carbon (RVC) electrodes and 3) by the combination of AO-EF. The BDD and RVC electrodes were fitted in a filter-press flow cell in recycle batch mode of operation. The experimental set up for the AO and EF processes consisted on two electrolyte compartments separated by a Nafion membrane with the dye contained in the anolyte and the catholyte, respectively. The combined AO-EF process used only one electrolyte compartment. The color and total organic carbon (TOC) removal were more efficient when the AO and EF processes were used separately than the combined process, AO-EF. The influence of current density and initial concentration of ferrous ions were examined. The lowest energy efficiency (208 kWh kg-1) with the EF process was found when-0.4 V vs Ag/AgCl was applied to a RVC electrode and the concentration of Fe 2+ was 1.0  10-4 mol dm-3 achieving total color and 74% of TOC removals in less than 90 min electrolysis. All proposed processes were able to promote high percentages of TOC removal following a pseudo first order kinetic oxidation. The BDD electrode was the most effective material to remove RB-5 dye within 7.5 min and presented the highest apparent rate constant (0.835 min-1) with 82% TOC removal within 30 min at an energy consumption of 291 kWh kg-1 and 41.1 mA cm-2 current density. In the case of the combined process AO-EF the electrodegradation rate of RB-5 was at least three times lower, apparent rate constant (0.269 min-1), and 32% of TOC was removed with a high EC (682 kWh kg-1). Therefore oxidation process applied separately was more efficient.