Fenton-like degradation of MTBE: Effects of iron counter anion and radical scavengers

Fenton-driven oxidation of methyl tert-butyl ether (MTBE) (0.11–0.16 mM) in batch reactors containing ferric iron (5 mM) and hydrogen peroxide (H2O2) (6 mM) (pH = 3) was performed to investigate MTBE transformation mechanisms. Independent variables included the forms of iron (Fe) (Fe2(SO4)3·9H2O and Fe(NO3)3·9H2O), H2O2 (6, 60 mM), chloroform (CF) (0.2–2.4 mM), isopropyl alcohol (IPA) (25, 50 mM), and sulfate (7.5 mM). MTBE, tert-butyl alcohol and acetone transformation were significantly greater when oxidation was carried out with Fe(NO3)3·9H2O than with Fe2(SO4)3·9H2O. Sulfate interfered in the formation of the ferro-peroxy intermediate species, inhibited H2O2 reaction, hydroxyl radical (OH) formation, and MTBE transformation. Transformation was faster and more complete at a higher [H2O2] (60 mM), but resulted in lower oxidation efficiency which was attributed to OH scavenging by H2O2. CF scavenging of the superoxide radical (O2-) in the ferric nitrate system resulted in lower rates of O2- reduction of Fe(III) to Fe(II), OH production, and consequently lower rates of MTBE transformation. IPA, an excellent scavenger of OH, completely inhibited MTBE transformation in the ferric nitrate system indicating oxidation was predominantly by OH. OH scavenging by HSO4-, formation of the sulfate radical (SO4-), and oxidation of MTBE by SO4- was estimated to be negligible. The form of Fe (i.e., counter anion) selected for use in Fenton treatment systems impacts oxidative mechanisms, treatment efficiency, and post-oxidation treatment of residuals which may require additional handling and cost.