Chemical Engineering Journal 171 (2011) 127–135 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Oxidative degradation of herbicide diuron in aqueous medium by Fenton’s reaction based advanced oxidation processes Mehmet A. Oturan a,∗ , Nihal Oturan a , Mohamed C. Edelahi a,b , Fetah I. Podvorica c , Kacem El Kacemi b a Université Paris-Est Marne-la-Vallée, Laboratoire Géomatériaux et Environnement, 5 Boulevard Descartes, Marne-la-Vallée Cedex 2, France b Laboratoire d’Electrochimie et de Chimie Analytique, Faculté des Sciences, Université Mohammed V Agdal, Boulevard Ibn Battouta, BP. 1114, Rabat, Maroc, Morocco c Chemistry Department of Natural Sciences Faculty, University of Prishtina, rr. “Nëna Tereze” nr. 5, 10 000 Prishtina, Kosovo article info Article history: Received 19 November 2010 Received in revised form 17 March 2011 Accepted 21 March 2011 Keywords: Phenylurea herbicides Fenton’s reagent Hydroxyl radicals Electro-Fenton AOPs Mineralization abstract Advanced chemical, photochemical and electrochemical oxidation processes based on catalytic gen- eration of hydroxyl radicals through Fenton’s reagent are applied to remove herbicide diuron from aqueous medium. To enhance the oxidation power of Fenton’s reagent, it was assisted photochemi- cally (photo-Fenton) or electrochemically (electro-Fenton). Kinetic analysis showed that the oxidation of diuron by hydroxyl radicals follows a reaction kinetic of pseudo-first order. The apparent rate con- stants values and mineralization degree of different photochemical processes revealed the superiority of the photo-Fenton process in degradation rate (kinetics) and that of electro-Fenton process in cost effectiveness and process efficiency. The absolute rate constant for diuron oxidation by hydroxyl rad- ical was determined as (4.75 ± 0.20) × 10 9 L mol -1 s -1 by competition kinetics method taking benzoic acid as reference compound. Electro-Fenton process exhibits a very fast degradation kinetics achiev- ing complete removal of 0.17 mM diuron in less than 6 min. The apparent current efficiency was determined; its maximum value of 28% at 0.6 h decreases with the treatment time to 11% at 3 h, i.e., when 89% of mineralization is achieved. When 300 mA was applied, higher mineralization efficiency of 96% was achieved. The photo-Fenton process exhibits also high mineralization efficiency reaching 97% TOC removal at 5 h under optimal operating conditions. Several oxidation by-products such as 3,[3,4-dichlorohydroxyphenyl]-1,1-methylurea, 3,[3-hydroxy 4-chlorohydroxyphenyl]-1,1-methylurea, 3-[trihydroxyphenyl]-1,1-dimethylurea, 3,[3-hydoxy-4-chlorophenyl]-1,1-methylurea, 3,[3-hydroxy-4- chlorophenyl]-1,1-dimethylurea, and dichloroaniline were identified by HPLC and LC–MS analyses evidencing two sites of attack of hydroxyl radical, the first being located on the aromatic ring and the sec- ond on the dimethylurea group. Based on the identification of aromatic intermediates, carboxylic acids and chloride ion released; a plausible diuron mineralization pathway is proposed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The economic growth together with worldwide technological and agricultural development has brought about environmental pollution. One of the greatest challenges nowadays is the abate- ment of a significant part of this pollution by destruction of toxic and hazardous organic pollutants. Very often, biological oxidation failed in eliminating toxic or recalcitrant organic micropollutants and physicochemical technologies such as flocculation, membrane filtration or adsorption on activated carbon just transferred them from one phase to another without destroying them. The concen- trate thus obtained necessitates a supplementary technique such as ∗ Corresponding author. Tel.: +33 1 49 32 19 60; fax: +33 1 49 32 91 37. E-mail address: Mehmet.Oturan@univ-paris-est.fr (M.A. Oturan). incineration for its elimination. Hence the needs for effective oxi- dation technologies with enhanced efficiency have consequently increased over the last two decades. There are several options for selecting an oxidation technol- ogy suitable for wastewater treatment such as wet air oxidation [1], supercritical water oxidation [2] incineration [3] and advanced oxidation processes (AOPs) [4–10]. The AOPs can be used for the treatment of relatively low level pollution in aqueous medium. They commonly use hydroxyl radicals ( • OH), extremely powerful short-lived oxidizing agents, able to oxidize organic compounds until complete mineralization. Fenton and Fenton based oxidation processes are among the AOPs. In the Fenton oxidation, • OH are generated from Fenton’s reagent, a mixture of H 2 O 2 and ferrous iron, according to the Fenton’s reaction [6,11]: Fe 2+ + H 2 O 2 → Fe 3+ + • OH + OH - (1) 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.03.072