Experimental design methodology applied to electro-Fenton treatment for degradation of herbicide chlortoluron Aida Kesraoui Abdessalem a,b , Nihal Oturan a , Nizar Bellakhal b,c , Mohamed Dachraoui b , Mehmet A. Oturan a, * a Universite ´ Paris-Est, Laboratoire Ge ´omate ´riaux et Ge ´ologie de l’Inge ´nieur, 5 bd Descartes, 77454 Marne la Valle ´e Cedex 2, France b Laboratoire de Chimie Analytique et E ´ lectrochimie, De ´partement de Chimie, Faculte ´ des Sciences de Tunis, Campus Universitaire, 2092Tunis El Manar, Tunisia c De ´partement de Chimie et de Biologie Applique ´es, Institut National des Sciences Applique ´es et de Technologie (INSAT), B.P. no. 676, 1080 Tunis Cedex, Tunisia Received 25 July 2007; received in revised form 19 September 2007; accepted 21 September 2007 Available online 2 October 2007 Abstract The degradation of herbicide chlortoluron in aqueous medium by electro-Fenton process using a carbon felt cathode and a platinum anode was studied. The great oxidation ability of this process is due to the large production of hydroxyl radical (OH  ) by electrochemically induced Fenton’s reagent. Hydroxyl radicals are very powerful oxidizing agents which react on organics up to complete mineralization. The influence of some experimental parameters such as initial concentration, current intensity and processing time on the degradation and mineralization rate of chlortoluron by hydroxyl radicals has been investigated. The evolution of chlortoluron concentration with processing time shows a pseudo first order kinetics (k abs = (4.8  0.2)  10 9 mol 1 Ls 1 ). A Doehlert matrix was applied for determination of the optimal working conditions. Optimal parameters for maximum mineralization efficiency (TOC removal ratio of 98%) was achieved after 8 h of treatment using a chlortoluron initial concentration of 0.125 mM and an applied current of 300 mA. The mineralization of aqueous chlortoluron solutions was confirmed by identification of the end-products such as carboxylic acids and inorganic ions. Their evolution during electro-Fenton treatment was studied. # 2007 Elsevier B.V. All rights reserved. Keywords: Chlortoluron; Electro-Fenton process; Mineralization; Experimental design; Hydroxyl radical 1. Introduction Since their discovery in the first 1950s, the phenylurea herbicides have been largely used to fight down the unwanted weeds. In fact, the phenylureas are thermosensitive and can be naturally degraded in isocyanats. But their degradation is slow in the environment [1]. They are so persistent and can be often found in water. The control networks of water detect regularly the amount of phenylureas superior to the regulate threshold. The highest values of chlortoluron were found in the cereals. It is absorbed by the roots and foliage and blocks the photosynthesis of the weeds of winter cereals [2]. The chlortoluron (Fig. 1) is one of the phenylurea herbicides mostly employed in the agricultural field and presents a half-life of 30–40 days in the soils and over 200 days in water [2]. A variety of techniques were used to treat the liquid effluent loaded with chlortoluron: UV/TiO 2 photo- catalysis [3,4], homogeneous photocatalysis [5], and biodegra- dation [6]. Recently, a new method of advanced oxidation processes (AOPs) called ‘‘electro-Fenton’’ has been successfully applied to mineralize the persistent organic pollutants [7–20]. In this work, the degradation of aqueous solutions of chlortoluron have been carried out by using an indirect electrochemical method based on the continuous production of hydrogen peroxide in the aqueous medium by the two-electrons reduction of oxygen on a carbon felt cathode [13,19]. Simultaneously, the Fe 2+ ions were generated by reduction of ferric ions which introduced initially as catalyst to the solution to be treated: O 2 þ 2H þ þ 2e  ! H 2 O 2 ; E 0 ¼ 0:695 V=SHE (1) Fe 3þ þ e  ! Fe 2þ ; E 0 ¼ 0:77 V=SHE (2) www.elsevier.com/locate/apcatb Available online at www.sciencedirect.com Applied Catalysis B: Environmental 78 (2008) 334–341 * Corresponding author. Tel.: +33 1 49329065; fax: +33 1 49329137. E-mail address: oturan@univ-mlv.fr (M.A. Oturan). 0926-3373/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2007.09.032