Photo-Fenton degradation of the herbicide 2,4-D in aqueous medium at pH conditions close to neutrality

Abstract

A theoretical and experimental study of the photo-Fenton degradation of the herbicide 2,4- dichlorophenoxyacetic acid (2,4-D) in water is presented. A kinetic model derived from a reaction sequence is proposed using the ferrioxalate complex as iron source for conditions of pH ¼ 5. The kinetic model was employed to predict the concentrations of 2,4-D, 2,4-dichlorophenol (2,4-DCP), hydrogen peroxide (HP) and oxalate (Ox) in a flat plate laboratory reactor irradiated with a solar simulator. Two types of incident irradiation levels were tested by different combinations of attenuation filters. The effects of the oxalate/Feþ3 molar ratio (Ox/Fe), the reaction temperature (T) and the 2,4-D/HP molar ratio (R) on the photo-Fenton process were also investigated. For low radiation level and operating conditions of R ¼ 50 and T ¼ 50 ºC, a 2,4-D conversion of 95.6% was obtained after 180 min. Moreover, the 2,4-D conversion was almost 100% in only 120 min when the system was operated under the same operating conditions and high radiation level. From the proposed model and the experimental data, the corresponding kinetic parameters were estimated applying a nonlinear regression method. A good agreement between the kinetic model and experimental data, for a wide range of simulated solar operating conditions, was observed. For 2,4-D, 2,4-DCP, HP and Ox concentrations, the calculated RMSE were 1.21 x 10-2, 5.45 x 10-3, 2.86 x 10-1 and 2.65 x 10-2 mM, respectively.