Reaction Mechanism and Kinetic Modeling of DEET Degradation by Flow-Through Anodic Fenton Treatment (FAFT)

The previously developed batch anodic Fenton treatment (AFT) technology has been successfully applied to degrade various pesticides in aqueous solution. The goal of this work is the development of a flow-through AFT system (FAFT) which is critical to bringing this technology into practical general use in the field. For this purpose, the degradation of DEET (N,N-diethyl-3-methylbenzamide), an insect repellent, and nine model amides was studied. Oxidation products of these compounds in FAFT were identified by GC/MS, and the results revealed that various -OH additions (most likely on the aromatic ring), quinone/keto product formation, and dimerization/bimolecular disproportionation are the major reaction pathways. This proposed overall reaction mechanism was then combined with the basic Fenton's mechanism to model the kinetics of various active species in FAFT including DEET, Fe2+, H2O2, and total iron under different reaction conditions. In addition, both initial and steady-state hydroxyl radical concentrations were measured in FAFT using benzoic acid as a chemical probe; the measured *OH concentrations were best-fitted exponentially. On the basis of the obtained [*OH] trend and the mass balance of the FAFT system, a simple FAFT model was developed to fit all of the degradation data of DEET and the model amides.