Heterogeneous Fenton oxidation using Fe-ZSM5 catalyst for removal of ibuprofen in wastewater

Heterogeneous Fenton oxidation using Fe-zeolite catalyst (of ZSM5 type) was investigated for the removal of ibuprofen (20 mg/L) in water. In particular, the effects of catalyst concentration, oxidant dosage, temperature, solution pH, and water matrix on pollutant conversion and mineralization were evaluated. The activity of leached iron species in solution was also measured to determine the contribution of the homogeneous reaction. Oxidation rate of ibuprofen obeyed a pseudo-first-order kinetics with respect to the pollutant concentration, and the apparent rate constant increased with catalyst and hydrogen peroxide concentrations in the investigated ranges (1-5 g/L of Fe-zeolite and 0.5-7 times the stoichiometric amount of oxidant). Energy activation of 53 kJ/mol was obtained from Arrhenius plot. However, the mineralization yield was not significantly improved by a too large excess of H₂O₂ or increase of temperature. In the selected conditions (25 °C, 4.8 g/L of catalyst, 2 times the stoichiometric amount of H₂O₂), 88% of ibuprofen and 27% of TOC were removed after 3 hours of reaction under "natural" pH conditions. Very low leaching (up to 0.2 mg/L) and negligible activity of leached iron in solution indicated that Fenton reaction was mainly induced by iron species on the catalyst surface. Degradation rate of ibuprofen was slower in wastewater effluent as compared to distilled water, mainly due to alkaline buffering and radical scavenging effects of organic and inorganic compounds present in the matrix. Mono- and multi-hydroxylated ibuprofen adducts were found as main oxidation intermediates -in line with free-radical mechanism- as well as 4-isobutylacetophenone from decarboxylation route.