Nihal Oturan

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

Abstract 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 polluted by toxic organic substances like pesticides. Chemically, these radicals are produced by the use of a mixture of (H 2 O 2 +Fe 2+ ), the so called Fentons reagent. In this work Fentons reagent is generated by electrochemistry in a catalytic way. The reaction of the hydroxyl radicals with pentachlorophenol (PCP) was studied. These radicals generated in situ in aqueous solution react with PCP and thus lead to its degradation. The evolution of the composition of the solution was followed by chromatographic analysis, COD analysis and the measurement of the total organic carbon (TOC) of the studied aqueous solution. Tetrachloro- o -benzoquinone and tetrachloro- p -benzoquinone (TCBQ) are the only aromatic intermediates identified. They result from the oxidation of the corresponding tetrachlorohydroquinones (TCHQ). Just like PCP, the TCBQs are degraded and disappear in their turn. The mineralization of the initial toxic substrate is confirmed on the one hand, by the regular decrease in quantity of the total organic carbon of the solution (TOC analysis) and on the other hand, by the quantitative release of chloride ions according to the electrical charge passed during electrolysis. The degradation of PCP appears relatively slow compared to that of the other organic pollutants studied by the electro-Fenton process and also to the degradation of other less substituted chlorophenols. The kinetic rate of the appearance of chloride ions is slower than that in the degradation of PCP. This phenomenon highlights the formation of chlorated aliphatic intermediates.

Degradation of chlorophenoxyacid herbicides in aqueous media, using a novel electrochemical method†

The degradation of five chlorophenoxyacid herbicides has been studied using an electrochemical method based on the Fenton reaction (simultaneous reduction of dioxygen and ferric ions). The method consists of electrosynthesizing OH˙ radicals, which react rapidly with chlorophenoxyacids in aqueous media. HPLC and GC-MS analysis show the formation of polyhydroxyphenols and quinones in a first step, and the complete destruction of the aromatic nucleus upon exhaustive electrolysis. This offers a possible way for the depollution of natural waters containing chlorophenoxyacid pesticide residues.

Olive Oil Mill Wastewater Treatment by the Electro-Fenton Process

Environmental Context. The combination of the Fenton’s reagent with electrochemistry (the electro-Fenton process) represents an efficient method for wastewater treatment. This study describes the use of this process to clean olive oil mill wastewater, which is a real environmental problem in Mediterranean countries. Contrary to the conventional methods which reduce the pollution by removing the pollutants from the wastewater, the electro-Fenton process is shown to fully destroy (mineralize) olive oil mill wastes in water without previous extraction and without addition of chemical reagents. Abstract. Treatment of olive oil mill wastewater is one of the most important environmental problems for Mediterranean countries. This wastewater contains many organic compounds like polyphenols, which are very difficult to treat by classical techniques. An advanced electrochemical oxidation process, the electro-Fenton process, has been used as a way of removing chemical oxygen demand and colour intensity from olive oil mill wastewater. Vanillic acid, which has been selected as a model compound, and olive oil mill wastewater have been completely mineralized by the electro-Fenton process with a carbon felt cathode, using Fe2+ ions as the catalyst.