UV-A assisted catalytic wet peroxide oxidation: Activity of iron minerals in the degradation of DEET

Abstract

The widespread use of insect repellent N,N’-diethyltoluamide (DEET), along with its low biodegradability, has made this an ubiquitous contaminant in waterbodies. This work explores the elimination of DEET (10 mg/L) in aqueous matrices employing natural iron minerals ilmenite (FeTiO3), hematite (Fe2O3), goethite (Fe(OOH)) and magnetite (Fe3O4) as low-cost catalysts in UV-assisted Catalytic Wet Peroxide Oxidation, using UV-A LEDs (λ: 395 nm) as radiation source in a 500 mL useful-volume reactor. Under the studied conditions, magnetite presented a higher activity, significantly superior to that of the other minerals. A parametric study evaluating the effect of the catalyst load, initial pH, H2O2 dose, UV irradiance and water matrix was performed. Magnetite is able to carry out DEET degradation working at circumneutral pH (pH: 5) with outstanding results in terms of DEET removal even in complex matrices such as river water and WWTP effluent. Furthermore, the catalyst presented an excellent stability. Still, under the optimal operating conditions of this study ([Fe3O4]: 500 mg/L, [H2O2]0: 61.1 mg/L, pH0: 5, T: 25ºC, t: 120 min), only 27.8% mineralization was reached in ultrapure water. Nonetheless, the remaining organic compounds are mainly short-chain organic acids (malonic, oxalic, acetic and formic acids), which account for 98.7% of the residual organic carbon. These compounds, which are readily biodegradable, present a lower phytotoxicity than that of DEET, demonstrating the potential of UV-CWPO for the elimination of this emerging contaminant.