Hydrogen peroxide and peroxymonosulfate intensifying Fe-doped NiC-Al2O3-framework-based catalytic ozonation for advanced treatment of landfill leachate: Performance and mechanisms

The biotreated effluent of landfill leachate still contains numerous refractory organic contaminants, which poses potential threats to human health and ecosystems. Influenced by landfill ages and other factors, the concentration of organic matter varies. Heterogeneous catalytic ozonation (HCO) is a promising technology for advanced wastewater treatment. Aiming to achieve the up-to-standard discharge of low-concentration landfill leachate (COD approximate to 108 mg center dot L-1) and improve the biodegradability of high-concentration landfill leachate (COD approximate to 1720 mg center dot L-1), the active component Fe was incorporated into a firm Ni-induced C-Al2O3-framework (NiCAF) composite support to synthesize a Fe-NiCAF catalyst for efficient catalytic ozonation. When the Fe-NiCAF dosage was 4 g center dot L-1, the gas flow rate was 0.5 L center dot min-1, and the ozone concentration was 20.0 mg center dot L-1, the COD of low-concentration landfill leachate effluent decreased to 43 mg center dot L-1, and the COD removal rate constant of low-concentration landfill leachate was 154% higher than that of pure ozone. For high-concentration landfill leachate with the BOD5/COD of 0.058, the COD removal efficiency in Fe-NiCAF/O3 increased from 39% to 57% compared with ozonation, and the effluent BOD5/COD increased to 0.282. Furthermore, the addition of hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) can further enhance the treatment performance of Fe-NiCAF/O3 process and different strengthening mechanisms were revealed. The results indicated that surface hydroxyls on the Fe-NiCAF catalyst surface were the main catalytic sites for ozone, and hydroxyl radical (center dot OH) and singlet oxygen (1O2) were identified as the main reactive oxygen species for the removal of organics in landfill leachate. Adding H2O2 can promote the generation of center dot OH for nonselective degradation of various organics, while PMS mainly enhanced the production of 1O2 to decompose macromolecular humus. This work highlighted an efficient Fe-NiCAF ozone catalyst and an innovative peroxide intensified HCO strategy for the advanced treatment of landfill leachate.