A solution with 0.38 mM of the pesticide propoxur (PX) at pH 3.0 has been comparatively treated by electrochemical oxidation with electrogenerated HO (EO-HO), electro-Fenton (EF), and photoelectro-Fenton (PEF). The trials were carried out with a 100-mL boron-doped diamond (BDD)/air-diffusion cell. The EO-HO process had the lowest oxidation ability due to the slow reaction of intermediates with OH produced from water discharge at the BDD anode. The EF treatment yielded quicker mineralization due to the additionalOH formed between added Fe and electrogenerated HO. The PEF process was the most powerful since it led to total mineralization by the combined oxidative action of hydroxyl radicals and UVA irradiation. The PX decay agreed with a pseudo-first-order kinetics in EO-HO, whereas in EF and PEF, it obeyed a much faster pseudo-first-order kinetics followed by a much slower one, which are related to the oxidation of its Fe(II) and Fe(III) complexes, respectively. EO-HO showed similar oxidation ability within the pH range 3.0-9.0. The effect of current density and Fe and substrate contents on the performance of the EF process was examined. Two primary aromatic products were identified by LC-MS during PX degradation.

h i g h l i g h t s Tebuthiuron and ametryn formulations degraded in a flow plant with BDD/air-diffusion cell. Growing oxidation power over single herbicide formulations: AO-H 2 O 2 < EF < SPEF. Two-stage kinetics in EF and SPEF due to the formation of Fe(II) and Fe(III) complexes. Similar profiles with lower oxidation ability for mixed herbicide formulations in SPEF. Identification of 4 heteroaromatic products in mixtures and release of sulfate and nitrate ions.

No abstract

The degradation and mineralization ability of electrochemical processes like electro-oxidation with electrogenerated H 2 O 2 (EO-H 2 O 2 ), electro-Fenton (EF) and UVA-assisted photoelectro-Fenton (PEF) has been comparatively studied for solutions of the herbicide S-metolachlor. Solutions of 100 mL have been treated using an undivided cell equipped with an air-diffusion cathode and a boron-doped diamond (BDD) anode. The effect of pH, current density, and Fe 2+ and S-metolachlor concentrations has been thoroughly studied. The total organic carbon removal profiles have demonstrated the feasibility of almost overall mineralization by EF and PEF after 9 h at 300 mA. The herbicide decays in both treatments informed about the complexation of Fe(III) ions formed from Fenton's reaction, which decelerated S-metolachlor removal. However, the high oxidation power of BDD anode allowed the gradual mineralization of such complexes. The identification of chlorinated and nonchlorinated degradation byproducts by GC-MS has allowed the proposal of main degradation routes.