Heterogeneous catalytic ozonation of natural organic matter with goethite, cerium oxide and magnesium oxide

Abstract

Synthetic goethite (FeOOH), magnesium oxide (MgO), and cerium oxide (CeO₂) were used as catalysts to enhance the ozonation of filtered raw river water. The UV absorbance (at 254 nm), dissolved organic carbon (DOC), molecular weight distribution (MWD), and also excitation–emission matrix fluorescence (EEM) changes of the filtered water were evaluated before and after catalytic ozonation and single ozonation to compare the degradation efficiency of natural organic matter (NOM) in the filtered water among the systems. The results showed that CeO₂ catalytic ozonation performed best on UV₂₅₄ removal. The addition of tert-butanol (TBA) in the systems had less effect on the removal of UV₂₅₄, indicating that UV₂₅₄ removal mainly resulted from direct oxidation. The mineralization of NOM in the filtered water by FeOOH catalytic ozonation and MgO catalytic ozonation was significantly better than that of single ozonation and CeO₂ catalytic ozonation. DOC removal depended on hydroxyl radical (HO˙) formation, which could also be verified by the changes of MWD. From the results of EEM, both fulvic acid and humic acid were oxidized effectively during catalytic ozonation and single ozonation while some differences among the systems emerged due to the different degradation mechanisms. Humic acid was oxidized followed by fulvic acid in single ozonation while they were oxidized simultaneously in the catalytic ozonation. Catalytic ozonation in the presence of MgO and FeOOH could oxidize humic acid and fulvic acid effectively due to the formation of HO˙. CeO₂ catalytic ozonation would reduce fulvic acid, which was rich in carboxylate more effectively than humic acid mainly through complexation. In brief, catalytic ozonation would shorten the reaction time and also increase the mineralization of organic matter in the filtered water compared with single ozonation. This study has a certain reference value for practical application of catalytic ozonation in the water treatment plants.