Oxidative degradation of aqueous solutions of imazapyr and imazaquin herbicides at room temperature and pH 3.0 has been investigated by Fenton, photo-Fenton and electro-Fenton processes. The high degradation power of these advanced oxidation processes is due to the large production of hydroxyl radicals (*OH), a strong oxidizing agent, by reaction between H2O2 and Fe2+ in the solution to be treated. These radicals are used to oxidize organic pollutants to aromatic and aliphatic intermediates through subsequent oxidation until complete mineralization. Degradation kinetics and evolution of the chemical composition of treated solutions in each process was followed by high performance liquid chromatography. The mineralization efficiency was determined by chemical oxygen demand analysis. The effect of experimental parameters such as initial herbicide concentration, hydrogen peroxide concentration, ferrous ion concentration and applied current on the degradation kinetics was examined. Better degradation and mineralization efficiency were observed in photo-Fenton and electro-Fenton processes compared with conventional Fenton process. A pseudo-first order kinetic model was employed to describe the result and determine the apparent and absolute rate constants of the reaction between hydroxyl radicals and herbicides.

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The degradation of the herbicide imazapyr has been carried out by three advanced oxidation processes involving iron ions as catalysts: Fenton's reagent, photoFenton and electro-Fenton. We show that all processes are rapid and efficient. The kinetic rate constant was found to be k=5.410 9 M 1 s 1 . The mineralization of imazapyr is almost complete using the photo-Fenton and electroFenton processes.

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