Novel approach based on removal of Metalaxyl by Advanced Oxidation process and hybrid-process: identification and mechanism pathway

International audience

English. In this study, three processes, Fenton, photo-Fenton, and photo-Fenton/adsorption hybrid, were evaluated for their ability to remove the fungicide Metalaxyl (MTX) from water. For the photo-Fenton and Fenton processes, three parameters (i.e. ferrous ion concentration, hydrogen peroxide and the pH of the aquatic medium) were optimized using the Doehlert three-parameter experimental design and response surface methodology. Metalaxyl degradation was determined by Liquid chromatography instrument coupled with a diode array detector. The mathematical models obtained were validated for each process. The optimal conditions were 225 mg L−1, mg L−1 and pH = 3.4 for the both Fenton and photo-Fenton process. Under these conditions, 22% of Metalaxyl degraded during the photo-Fenton process and 20% during the Fenton process. The adsorption/photo-Fenton hybrid process was developed to achieve total removal of Metalaxyl using activated carbon elaborate from vegetable waste. This objective was reached after 240 min using a two-stage process, 120 min per stage, under the following conditions: =25 mg L−1, 382 mg L−1and =100 mg L−1 for the first stage and =10 mg L−1, 133 mg L−1and = 34 mg L−1 for the second one. A novel combination of a quick, easy, cheap, effective, rugged, and safe extraction method, pre-concentration by evaporation and Gas Chromatography coupled with triple quadrupole Mass Spectrometry analysis was used to identify the photo-degradation by-products at ultra-trace levels. Five by-products were identified and three possible degradation pathways were also proposed.