Chemical kinetic modeling of organic pollutant degradation in Fenton and solar photo-Fenton processes

Abstract The oxidation of organic pollutants by Fenton's reagent is commonly considered as a single-stage process that conforms to pseudo first-order kinetics. However, pollutant oxidation would exhibit a two-stage pattern when the initial dosage of Fenton's reagent is sufficiently high. This study investigated the fast oxidation kinetics of a model pollutant, malachite green (MG), in Fenton process in real time using continuous on-line spectrophotometric detection. A chemical kinetic model was further developed, which could well predict the effect of initial concentrations of Fe2+, H2O2, and MG on the degradation of MG in Fenton and solar photo-Fenton processes. The model could also be adapted to model the kinetics of MG mineralization. Modeling results reveal that the significant enhancement in the degradation rate of MG in the second stage of Fenton process by sunlight irradiation was contributed mainly by the production of hydroxyl radicals from H2O2 photolysis. The chemical kinetic model also performed well in describing the degradation and mineralization kinetics of carbendazim and thiabendazole in solar photo-Fenton process. The improved understanding on the fast kinetics of pollutant degradation and the chemical kinetic model developed could help optimize the treatment conditions for organic pollutants in Fenton and solar photo-Fenton processes.