Methomyl degradation in aqueous solutions by Fenton's reagent and the photo-Fenton system

The chemical degradation of pesticide methomyl in water by Fenton (H2O2/Fe2+) and photo-Fenton (H2O2/Fe2+/UV) processes was investigated. A laboratory set-up was designed to evaluate and select the optimal oxidation process. The degradation rate is strongly dependent on the pH, initial concentrations of the pesticide, H2O2, Fe2+, and [H2O2](0)/[Fe2+](0) ratio. The effect of these parameters has been studied and the optimum operational conditions of these two processes were found. The optimum conditions were obtained at pH 3 for the H2O2/Fe2+ and H2O2/Fe2+/UV. The kinetics of degradation was found to follow first-order reaction rules. The photo-Fenton system proved to be the most efficient and occurs at a much higher oxidation rate than Fenton system and allows achieving 100% degradation of methomyl in 30 min of reaction time. The results of the study showed that photo-Fenton process was an effective and economic treatment process for methomyl under acidic conditions by producing higher mineralisation efficiency in a relatively short radiation time compared to Fenton process. (C) 2007 Elsevier B.V. All rights reserved.