Production of hydroxyl radicals by electrochemically assisted Fenton's reagent - Application to the mineralization of an organic micropollutant, pentachlorophenol

Hydroxyl radicals are very powerful oxidizing agents. They are involved in hydroxylation reactions, in biological and atmospheric phenomena. A recent application of these radicals is their use in decontamination of water poll uted by toxic organic substances like pesticides, Chemically, these radical s are produced by the use of a mixture of (H2O2 + Fe2+), the so called Fent on's reagent. In this work Fenton's reagent is generated by electrochemistr y in a catalytic way, The reaction of the hydroxyl radicals with pentachlor ophenol (PCP) was studied. These radicals generated in situ in aqueous solu tion react with PCP and thus lead to its degradation. The evolution of the composition of the solution was followed by chromatographic analysis, COD a nalysis and the measurement of the total organic carbon (TOC) of the studie d aqueous solution. Tetrachloro-o-benzoquinone and tetrachloro-p-benzoquino ne (TCBQ) are the only aromatic intermediates identified. They result from the oxidation of the corresponding tetrachlorohydroquinones (TCHQ). Just li ke PCP, the TCBQs, are degraded and disappear in their turn. The mineraliza tion of the initial toxic substrate is confirmed on the one hand, by the re gular decrease in quantity of the total organic carbon of the solution (TOC analysis) and on the other hand, by the quantitative release of chloride i ons according to the electrical charge passed during electrolysis. The degr adation of PCP appears relatively slow compared to that of the other organi c pollutants studied by the electro-Fenton process and also to the degradat ion of other less substituted chlorophenols. The kinetic rate of the appear ance of chloride ions is slower than that in the degradation of PCP. This p henomenon highlights the formation of chlorated aliphatic intermediates. (C ) 2001 Elsevier Science B.V. All rights reserved.