The degradation of the azo dyes azobenzene, pmethyl red and methyl orange in aqueous solution at room temperature has been studied by an advanced electrochemical oxidation process (AEOPs) under potentialcontrolled electrolysis conditions, using a Pt anode and a carbon felt cathode. The electrochemical production of Fenton's reagent (H 2 O 2 , Fe 2+ ) allows a controlled in situ generation of hydroxyl radicals ( · OH) by simultaneous reduction of dioxygen and ferrous ions on the carbon felt electrode. In turn, hydroxyl radicals react with azo dyes, thus leading to their mineralization into CO 2 and H 2 O. The chemical composition of the azo dyes and their degradation products during electrolysis were monitored by high performance liquid chromatography (HPLC). The following degradation products were identified: hydroquinone, 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol, 1,3,5-trihydroxynitrobenzene and p-nitrophenol. Degradation of the initial azo dyes was assessed by the measurement of the chemical oxygen demand (COD). Kinetic analysis of these data showed a pseudo-first order degradation reaction for all azo dyes. A pathway of degradation of azo dyes is proposed. Specifically, the degradation of dyes and intermediates proceeds by oxidation of azo bonds and aromatic ring by hydroxyl radicals. The results display the efficiency of the ElectroFenton process to degrade organic matter.

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Aqueous solutions of organophosphorus pesticides were completely mineralized via in-situ generated hydroxyl radicals (HO · ) by the Electro-Fenton process. Formation of Fenton's reagent (H 2 O 2 , Fe 2+ ) was carried out by simultaneous reduction of O 2 and Fe 3+ on carbon cathode in acidic medium. The electrochemistry combined with Fenton's reagent provides an excellent way to continuously produce the hydroxyl radical, a powerful oxidant. We demonstrate the efficiency of the ElectroFenton process to degrade three organophosphorus insecticides: malathion, parathion ethyl and tetra-ethyl-pyrophosphate (TEPP). Degradation kinetics and removals of chemical oxygen demand (COD) have been investigated. Here we show that the mineralization efficiency was over 80% for three organophosphorus pesticides.