The photoelectro-Fenton degradation of 2.5 l of solutions containing herbicide
mecoprop (2-(4-chloro-2-methylphenoxy)-propionic acid) up to 0.64 g l
−1, 0.05 M Na
2SO
4 and 0.5 mM Fe
2+ of pH 3.0 has been studied using a flow plant with a one-compartment filter-press electrolytic reactor with a boron-doped diamond (BDD) anode and an O
2-diffusion cathode, both of 20-cm
2 area, coupled to either a UVA or solar photoreactor. Electrolyses performed in batch at low constant current density yield overall mineralization in both methods, although the process is much faster and less expensive with solar light. Under these conditions, the degradation rate and efficiency increase strongly with rising
mecoprop content. The kinetics for the herbicide decay follows a pseudo-first-order reaction. Mecoprop reacts rapidly with hydroxyl radical (
![radical dot](http://www.sciencedirect.com/scidirimg/entities/rad)
OH) produced from Fenton's reaction between Fe
2+ and H
2O
2 electrogenerated at the cathode to yield 4-chloro-
o-cresol, 2-methylhydroquinone and 2-methyl-
p-benzoquinone as primary reaction products. Fe
3+-oxalato and Fe
3+-acetato complexes are detected as the most persistent final products. Overall mineralization is attained because Fe
3+-oxalato complexes are efficiently photodecomposed by solar irradiation, whereas Fe
3+-acetato complexes are slowly destroyed by
![radical dot](http://www.sciencedirect.com/scidirimg/entities/rad)
OH formed at the BDD anode from water oxidation. The initial chlorine is released as Cl
−, which is slowly oxidized to Cl
2 on BDD. Photoelectro-Fenton with solar light appears to be a viable method to remove chlorophenoxy herbicides in wastewaters at industrial scale.