Nihal Oturan 1 , Mohamed C. Edelahi 1 , Mehmet A. Oturan 1 ,

1. Comparative study of degradation of herbicide diuron residues in water by various Fenton’s reaction-based advanced oxidation processes Nihal Oturan1, Mohamed C. Edelahi1, Mehmet A. Oturan1, Jean-Jacques Aaron1, Fetah I. Podvorica2, Kacem El Kacemi31Université Paris-Est Marne-la-Vallée, Laboratoire Géomatériaux et Environnement (LGE), France 2 Chemistry Department, Natural Sciences Faculty, University of Prishtina, Prishtina, Kosovo3 Laboratoire d’Electrochimie et de Chimie Analytique, Faculté des Sciences, Université Mohammed V Agdal, Rabat, Maroc

2. INTRODUCTION • Due toworlwideagricultural development, contamination of natural waters by pesticides at trace level • Use of advanced oxidation processes (AOPs) Fenton’s reaction- based for treating low levels of pollution in waters, : Fe 2+ + H2O2 → Fe3+ + OH + OH- • Very powerful, short-lived hydroxy (OH) radicals are generated • To eliminate chemicals and avoid wasting side-reactions, possibility of catalysing Fenton’s reaction either photochemically (photo-Fenton) or electrochemically (electro-Fenton). • Diuron: widely-used, water-soluble phenyl urea herbicide, very persistent in soils, able to form toxic degradation by-products: • contaminates soils and waters at the mg L-1 level & included in the EU list of priority hazardous substances • Development of several methods for diuron degradation: ozonation, chemical oxidation, solar photocatalytic degradation with TiO2 etc...

3. GOALS OF THE WORK ✓ Comparison of the direct Fenton reaction, photochemical degradation (photo-Fenton) and electrochemical oxidation (electro-Fenton) AOPs for treatment of diuron-containing waters ✓ Study of the diuron disappearance kinetics , formation and evolution of oxidation reaction intermediates, and mineralization efficiency for these various AOPs ✓ Proposition of a degradation pathway for diuron mineralization in water

4. EXPERIMENTAL ✓Photochemical experiments: quartz photoreactor (40 W low-pressure UV Hg lamp - λ = 253.7 nm) ✓Electro-Fenton reaction: electrolysis in a 250-mL three-electrode electrochemical cell with a potentiostat-galvanostat, under current intensity-controlled conditions (I = 60, 100, 200 and 300 mA) ✓Monitoring of Diuron reaction kinetics and product formation by HPLC-UV DAD - Mobile phase: water-methanol 40/60 v/v ✓Identification of Diuron hydroxylated derivatives: LC-MS – Mobile phase: methanol/water/formic acid 59.5/39.5/1 v/v/v ✓ Diuron mineralization efficiency: COD analyses (French AFNOR NFT-90-101 norm) on 30-mL samples withdrawn from solutions at different charge intervals

5. RESULTS Diuron mineralization by the photochemical processes (1) • Kinetic study • Diuron photochemical degradation kinetics in aqueous solutions by different photochemical processes: UV alone (▲);UV/H2O2 (■); UV/ H2O2 /Fe3+ (◊).

6. Diuron mineralization by the photochemical processes (2) Apparent (pseudo-1st order) and absolute (2nd order) rate constants of diuron oxidative degradation reaction for different photochemical processes. • Diuron decay curves fit very wellpseudo-1st order kinetics • Increase of the kappvalues according to the order: UV alone < UV/H2O2 < UV/H2O2 /Fe3+(photo-Fenton)

7. Diuron mineralization by the photochemical processes (3) • COD abatement as mineralization efficiency parameter • Highest mineralization efficiencies during the diuron photo-Fenton process (generation of powerful OH radicals by different reactions) • Increase of the mineralization efficiency from 73 to 85 % and from 86 to 93.5 % for 2-h and 5-h treatment times, respectively with the H2O2 concentration from 2.5 to 10 m M. • In the case of Fe (III) photolysis (Fe3+/UV process, without H2O2), increase of the mineralization efficiency from 26 to 39 % and from 48 to 56 % for 2-h and 5-h treatment times, respectively, with the increase of [Fe3+] from 0.1 to 1 m M.

8. Diuron mineralization by the electro-Fenton process (1) • Kinetic study • Oxidative degradation kinetics of diuron (0.17 mM) in a pH 3 aqueous solution by the electro-Fenton process. I = 60 mA. [Fe3+] = 0.2 mM - Inset: plot of Ln(C0/Ct) = f (t): pseudo-1st order behaviour of the reaction kinetics. • Value of k app = 0.25 min-1 , close to k appof the photo-Fenton process.

9. Diuron mineralization by the electro-Fenton process (2) • Mineralization of diuron aqueous solution • Mineralization efficiency values: 49% and 93 %, respectively, for 0.5 and 3 h of treatment (electrolysis at I = 100 mA). • Disappearance of diuron and its intermediates: formation of aliphatic compounds (not detectable by HPLC-UV) and, simultaneously, mineralization process during the electro-Fenton treatment. • Diuron mineralization by the electro-Fenton process: formation of CO2 and inorganic ions (Cl- , NO3-) due to the presence of Cl and N atoms in the diuron molecule.

10. Diuron mineralization by the electro-Fenton process (3) • Degradation pathway for diuron mineralization by OH radicals

11. CONCLUSIONS ✓ Diuron can be mineralized by Fenton, photo-Fenton and electro- Fenton processes. ✓ In Fenton’s oxidation (Fe2+/H2O2): enhancement of diuron mineralization efficiency by increasing the H2O2 concentration ✓For photochemical processes: much faster diuron oxidation and mineralization rates in water with the Fe3+/ H2O2 /UV system than with the H2O2 /UV and the direct UV ones. ✓ Photo-Fenton process: quasi-complete mineralization of diuron (mineralization efficiency = 93.5% for a 5-h treatment). ✓Electro-Fenton process: rapid degradation kinetic of diuron in water, with complete disappearance of diuron (0.17 mM) in a few min.