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The use of a novel electrochemical oxidation system is investigated for in situ generation of hydrogen peroxide, which constitutes the major reactant for hydroxyl radical (OH•) production via the Fenton reaction. The novel electro-Fenton (EF) “filter” is comprised of a stack of carbon anodic and cathodic electrode pairs, for operation in continuous mode, with potential applications in elimination of toxic organic substances (e.g., pesticides, pharmaceuticals) from drinking and similar water sources. Experiments are performed to assess the performance of three types of electrodes (made of woven carbon fibers, loose carbon fibers, and powdered carbon) in the synthesis of hydrogen peroxide by supplying to the system a low voltage direct current. The efficiency of H2O2 electro-generation as a function of various process parameters (i.e., electrode potential, solution pH, ionic strength) is studied for the most promising carbon material (i.e., loose carbon fibers). The results indicate that the optimal cathodic potential for H2O2 generation is 1.3 V vs Ag/AgCl reference electrode at pH 3, with initial mean dissolved oxygen concentration 8.5 mg L–1. Under these conditions, the average current density and average current efficiency are 5.2 A·m–2 and 70%, respectively. Reduced electrolyte (Na2SO4) concentration significantly affects the H2O2 electrogeneration rate, whereas increased solution pH leaves the current efficiency unaffected. Research is ongoing regarding optimization of the EF “filter” and the effective impregnation (in the porous cathodic electrodes) of iron nanoparticles, which mediate the continuous degradation of organic substances.

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New results are presented on the preparation and performance of iron-impregnated carbon electrodes for a novel electro-Fenton "filter"-type device, reported in a previous publication. Two composite Fe/carbon-felt electrodes were prepared via different procedures: one prepared under oxidizing conditions (i.e., dissolved oxygen) through immersion of carbon felt in an iron ethanolic solution (CF m -Fe), and another prepared under reduced oxidative conditions (nitrogen, ammonia, etc.) leading to in situ formation of iron nanoparticles on the carbon surface (CF m -nFe). The cathodes were characterized by X-ray diffraction (XRD), N 2 adsorption−desorption (BET), scanning electron microscopy (SEM), Raman microspectroscopy, and linear sweep voltammetry (LSV). The stability and oxidation performance of these electrodes were evaluated by measuring the leaching of iron species and the degradation in aqueous medium of a common pharmaceutical compound (diclofenac), respectively. The results show that the flow-through operation leads to increased solute removal, attributed to the enhanced electrosorption on the charged electrodes and the synergistic degradation/mineralization of diclofenac due to Fenton reactions on the composite cathodes. The CF m -nFe composite cathode was the most stable, exhibiting high sorption capacity (59.2 mg DCF g CFm −1) and significant degradation/mineralization efficiency (63.7 and 31.6%, respectively) at low applied potential (1.0 V/Ag/AgCl), neutral pH and high initial pollutant concentration (∼34 mg L −1 ). The results demonstrate the capability of the electro-Fenton process, implemented in the novel "filter"-type device, to decontaminate neutral waters polluted by diclofenac and similar organic compounds with no addition of chemicals and with reduced energy expenditure. Research and development (R&D) needs are also outlined.

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