Keywords:Boron-doped diamond Electrochemical oxidation Electro-Fenton process Filter-press flow cell Reactive Black 5 dye Reticulated vitreous carbon 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 of 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 colour 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 colour 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.
Reactive Blue 19 (RB‐19) dye has a low fixation efficiency, a long half‐life and high toxicity. It is easily loss during the cleaning of textiles and can remain in the environment for a long time, causing serious environmental problems if not removed. This study reports the degradation of RB‐19 by: 1) direct electrochemical degradation with boron‐doped diamond (BDD) electrodes and 2) combined processes using BDD and reticulated vitreous carbon (RVC) electrodes that generate H2O2. The direct degradation uses different current densities and concentrations. High currents densities, longer electrolysis times and low volumetric flow rates favour RB‐19 degradation, removing total colour and 100 % TOC after 5 and 60 min, respectively. At a current density of 41 mA cm−2 and a volumetric flow rate of 20 dm3 h−1, the energy consumption to degrade 20 mg dm−3 of RB‐19 was 279 kWh kg−1. The TOC removal of RB‐19 dye combining BDD and RVC at a current density of 41 mA cm−2 was below 72 % after 90 min and the energy consumption increased to 612 kWh kg−1. The higher energy consumption observed during the combined process suggests that the direct degradation process at low volumetric flow rates is more efficient than the combined process.
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