Removal of procion red mx-5b by electrochemical technologies

The textile and paper industries require large volumes of water and produce effluents that contain large quantities of organic compounds and inorganic salts and have high COD and colour levels. In particular, due to the presence of reactive dyes, colour removal is the major problem in dealing with these effluents. These reactive dyes should be removed in wastewater due to the damage they cause to the environment. However, synthetic dyes contain one or more functional groups and complex aromatic structures which make them very difficult to biodegrade. Traditional physico-chemical methods for the treatment of dyeing wastewater, including adsorption, coagulation and filtration enable fast decolourization, nevertheless these processes generate large volume of sludge to be disposed and/or need the regularly regeneration of adsorbent materials. These factors lead to an increase in the operational costs and therefore, it is necessary to look for new efficient processes that minimize waste generation. In this context, Advanced Oxidation Processes (AOPs) such as Fenton’s reagent, ozonation and photochemical oxidation provide effective colour removal and complete destruction of synthetic dyes molecules avoiding the potential formation of wastes. Among the AOPs, the Electrochemical Advanced Oxidation Processes (EAOPs) are a promising alternative because they are environmentally clean and can produce large amount of hydroxyl radicals under control of applied current. In these processes, the hydroxyl radicals can be produced by anodic oxidation (AO) of water using high O2 overvoltage anodes such as boron-doped diamond (BDD) anode [1]. Alternatively, hydroxyl radicals production can take place in solution bulk through electrochemically assisted Fenton’s reaction (EF), where hydrogen peroxide is generated in situ from the two-electron reduction of O2 on carbon cathodes such as gas diffusion electrodes (GDEs) or graphite felt [2]. Thus, this work presents the comparative degradation of Procion Red MX-5B, selected as model dye, by AO using BDD or DSA anode and EF using a graphite felt cathode. The influence of the main experimental variables was explored (current density, flow rate, supporting electrolyte…). The decay kinetics, decolorization rate and mineralization degree were compared to clarify the oxidation power of both methods.