Improved mineralization by combined advanced oxidation processes

Different single treatments and a combined process based on two advanced oxidation processes, catalytic wet peroxide oxidation and photocatalysis, have been tested for the purpose of achieving complete mineralization using phenol as target compound at medium-range concentration (200 mg L−1). The heterogenous catalysts that were used were a home-made activated carbon-supported iron catalyst (FeCN), and the commercial Aeroxide titania P25. An important improvement in the rate and percentage of TOC removal was achieved by combining both catalysts in a hybrid process based on a mixture of FeCN and TiO2 P25 (50:50 wt.%) in the same photoassisted reactor in ambient conditions. TOC evolution has been modelled for all the treatments for comparative purposes. The hybrid process allowed a highly efficient use of hydrogen peroxide with the almost complete oxidation of phenol to CO2 and H2O by using the theoretical stoichiometric amount of H2O2. Among the different advantages of this hybrid process is the rapid and effective degradation of the aromatic compounds adsorbed onto the Fe/CN catalyst surface as a consequence of synergistic effect of the two catalysts in the presence of irradiation light in ambient conditions, achieving a higher degree of mineralization of short-chain organic acids that are resistant and refractory to CWPO treatment. Finally, the stability and durability of this catalytic mixture (FeCN + titania P25) in hybrid mode have been examined through four consecutive cycles. A constant organic matter removal was observed during the last three consecutive cycles in which 90% of total organic carbon conversion was achieved.

Graphical abstractTOC conversions and Fe leaching after 5 h reaction time for the consecutive hybrid runs.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Improved mineralization by combined CWPO with Fe/AC catalysts and photocatalysis with TiO2. ► A very low iron leaching and effective mineralization of the short-chain organic acids by photocatalytic oxidation. ► Hybrid process presents a more efficient use of H2O2. ► Two important goals: photodegradation of the adsorbed aromatics onto Fe/CN catalyst and fairly high degree of mineralization.