Photo-Fenton degradation of the insecticide esfenvalerate in aqueous medium using a recirculation flow-through UV photoreactor

Highlights: ► The photo-Fenton reaction provides an efficient process by which to degrade esfenvalerate in aqueous suspensions. ► Photo-Fenton oxidation with Fe3+ is more efficient in degrading esfenvalerate than the Fe2+-based reaction. ► Esfenvalerate was degraded most efficiently by photo-Fenton reaction in the presence of 5 mM Fe3+ complex and 25 mM hydrogen peroxide at pH 2.5. ► The degradation of esfenvalerate by photo-Fenton (Fe3+) generates organic by-products. ► Organic compounds present in commercial esfenvalerate-based insecticides affect the degradation process. - Abstract: The aim of the study was to evaluate the efficiencies of photo-Fenton (Fe2+) and (Fe3+) processes in the degradation of high-concentrations of esfenvalerate (in the form of aqueous emulsion of a commercial formulation) using a recirculation flow-through photoreactor irradiated with UV light from a 15 W lamp (254 nm emission peak). The results obtained using a basic photo-Fenton (Fe2+) reaction (esfenvalerate 17 mg L−1; ferrous sulphate 1 mM; hydrogen peroxide 25 mM; pH 2.5) were compared with those acquired when ferrioxalate (1, 3 or 5 mM) served as the iron source. Degradation of the active component of the commercial formulation was significantly greater, and the rate of oxidation more rapid, using a photo-Fenton (Fe3+) process compared with its Fe2+ counterpart. The most efficient degradation of the insecticide (75% in 180 min) was achieved with a reaction mixture containing 5 mM ferrioxalate. However, under the same experimental conditions, degradation of pure esfenvalerate preceded much faster (99% in 60 min) and was 100% complete within 180 min reaction time.