Modified Fenton's reagent: The use of complexed ferrous iron in the degradation of methyl tert-butyl ether (MTBE) in aqueous solutions and soil matrices

The degradation and kinetics of methyl tert-butyl ether (MTBE) by hydrogen peroxide at near-neutral pH were investigated using classical Fenton's reagent and a modified Fenton's reagent (ferrous iron chelated with ethylenediaminetetraacetic acid, EDTA). Dilute aqueous MTBE (100–400 μg/L) solutions were degraded in batch and continuously hydrogen peroxide-fed stirred-tank reactor (CFSTR) with Fe (II) and Fe(II)-EDTA present as a catalyst at constant pH. The modified Fenton's reagent significantly increased the degradation of MTBE (6.2–71%) in a batch reactor at near-neutral pH (5.5 to 7.5) when compared to classical Fenton's reagent (0.69–5.09%) under the same conditions. The modified Fenton's reagent extended the normal operating pH range for classical Fenton's reagent from 3–4 to 3–8.5. The reaction was more effectively controlled using the CFSTR. MTBE degradation of up to 99% in 60 minutes was achieved in the CFSTR with 0.17M hydrogen peroxide fed to the reactor at 40 mL/hr. A MTBE degradation mechanism by hydroxyl radicals is presented and rate constants were determined. The MTBE degradation rate constants were found to be pseudo-first order between pH 5.5 and 7.5 using Fe(II)-EDTA.; The degradation of MTBE in soil slurries (12.58 soil/L) was also investigated using Ottawa sand, Kaolin clay, and Na-Montmorillonite clay in CFSTR. Fe(II)-EDTA was present as a catalyst in 0.01M sodium bicarbonate buffer solution. MTBE degradation of up to 99% was achieved in the CFSTR in 60 minutes.; MTBE and degradation product concentrations were measured using a purge-and trap GC-FID method. Two major oxidation by-products were observed in the aqueous solution and soil slurries, tert-butyl formate and tret-butyl alcohol. Decomposition of hydrogen peroxide by Fe(II)-EDTA contributed to a decreased extent of MTBE removal, i.e., mole MTBE destroyed per mole of hydrogen peroxide consumed. The dissolved oxygen concentration increased significantly with time as the hydrogen peroxide decomposed.