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Contribution à l'étude de dégradation in situ des pesticides par procédés d'oxydation avancés faisant intervenir le fer. Application aux herbicides phénylurées

Abstract : Advanced oxidation processes (AOP) permit the total degradation (mineralization) in aqueous solutions of hazardous organic molecules for human being and for the environment. Electro-Fenton process which made part of AOP has been applied to phenylureas herbicides. Performances of this process has been compared with other AOP involving the use of iron (ferrous or ferric) such as Fenton reagent and photo-Fenton process.

In the case of studied herbicides (diuron, monuron and fenuron), it has been shown that mineralization rate by Fenton process (Fe2+/H2O2) increase with the increase of reagents concentrations and time of reaction. In the case of the photochemical degradation (UV irradiation), the degradation and mineralization rates are very low. The degradation rate of parent molecules and mineralization efficiency of studied herbicides can be enhanced significantly by coupling photochemistry with Fenton reagent (Fe2+/H2O2). This coupling allow also the decrease of irradiation time and saving of electrical energy. Concerning the Electro-Fenton process, the kinetics of degradation and mineralization depends on experimentals parameters such as catalysis concentration, applied current intensity, etc.

The reactivity of chlorophenylureas herbicides toward hydroxyl radicals is a function of the number of chlorine atoms substituted on the aromatic cycle. Degradation rate increase as following: diuron (2 Cl substituted), monuron (1 Cl substituted) and fenuron (no Cl substituted). Mineralization study of these herbicides showed that the abatement rate of organic carbon in term COD were up to 90% for a treatment time of 3 hours in the case of Electro-Fenton process. A general pathway for the mineralization of chlorophenylureas herbicides is initiated by the attack of the hydroxyl radicals of the parent molecule on two positions: the N-terminal group and the aromatic cycle leading to a several by-products. Several aromatic by-products which are mainly issued by an oxidation of the N-terminal group followed by a hydroxylation of the aromatic cycle and substitution of chlorine atoms on the aromatic cycle have been identified. Further oxidations steps involve oxidative opening of the aromatic ring, leading to carboxylic acids and inorganic ions.

A comparison of the mineralization performances of different studied processes showed that photo-Fenton and Electro-Fenton processes permit to reach a very important mineralization rate (93%). The Electro-Fenton process can be considered the more efficient techniques with no use of chemicals and low energy consumption.
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https://tel.archives-ouvertes.fr/tel-00008352
Contributor : Mohamed Chakib Edelahi <>
Submitted on : Thursday, February 3, 2005 - 5:31:41 PM
Last modification on : Thursday, January 11, 2018 - 6:19:28 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:19:34 PM

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Mohamed Chakib Edelahi. Contribution à l'étude de dégradation in situ des pesticides par procédés d'oxydation avancés faisant intervenir le fer. Application aux herbicides phénylurées. Autre. Université de Marne la Vallée, 2004. Français. ⟨tel-00008352⟩

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