Study of simultaneous electro-Fenton and adsorption processes in a reactor containing porous carbon electrodes and particulate activated carbon

Abstract

• Novel electro-Fenton reactor with porous carbon electrodes and activated carbon (AC). • • OH electrochemical generation was observed in the absence of Fe(II). • Increased electrical conductivity and • OH production at high levels of AC packing. • The effect for simultaneous adsorption and electro-Fenton process was studied. • Promising process for potabilization or wastewater treatment at circumneutral pH. Although electro-Fenton wastewater treatment processes are particularly attractive for their high oxidation power, they are seriously limited by the low pH values that are required for the process, the subsequent neutralization of acid and the addition and removal of iron chemicals. In this work, a study on the design, characterization and performance of a novel electro-Fenton reactor, shows that there is a simultaneous effect that can overcome these limitations when combining activated carbon (AC) adsorption and electro-Fenton effects, while working at same time under neutral pH conditions. The reactor arrangement proposed, involves a cation exchange resin that continuously supplies Fe(II) ions to a chamber containing an AC adsorption bed that is positioned between two concentric porous carbon electrodes. Preliminary experiments assessing the 2e - electrochemical reduction of dissolved oxygen to produce H 2 O 2 in the reactor in the absence of AC, showed that while the concentrations of electro-generated peroxide are, as expected, proportional to the current density, they are inversely related to the current efficiency values. A fluorescence study of hydroxyl radical ( • OH) production on the other hand, showed that in the absence and in the presence of iron ions, the corresponding concentration of • OH is 0.800 and 1.057 µM, respectively. Experiments with the reactor using varying amounts of AC, resulted not only in coupled adsorption effects characterized by a removal capacity that increases with the amount of AC, but also in increased electrical conductivity and higher electro-Fenton activity that is probably related to an improved electrical contact between the AC particles and the polarized carbonaceous electrode surface. The performance of the electro-Fenton reactor proposed in this work, was finally evaluated in terms of the removal of a model pollutant dye in both synthetic and real secondary effluents using different AC packed levels. Consistent with previous experiments, the fully compacted AC presented the higher removal rates due to the simultaneous effect of the adsorption of the pollutant and the coupled electro-Fenton degradation process.