Oxidative degradation of landfill leachate by catalysis of CeMnOx/TiO2 in supercritical water: Mechanism and kinetic study

- The influence of operating conditions on TOC and NH3-N removal efficiencies was investigated.
- Significant co-oxidation effect of methanol and landfill leachate during SCWO was detected.
- The addition of synthesized CeMnOx/TiO2 catalysts enhanced the removal efficiencies of TOC and NH3-N during SCWO.
- Possible reaction mechanisms were developed for the catalytic process.

Landfill leachate is a typical refractory wastewater that contains high concentration of organic pollutants. In this work, we investigated the treatment of landfill leachate by supercritical water oxidation (SCWO) in a batch reactor. The effects of temperature (T, 450-600 °C), oxidation coefficient (OC, 1.2-3.4), reaction time (t, 60-600 s) and pH (4.13-8.05) on total organic carbon (TOC) removal efficiency (TRE,%) and ammonia nitrogen (NH3-N) removal efficiency (NRE,%) were analyzed. TRE and NRE increased remarkably with increasing temperature and OC. At 3.4 OC and 600 °C, 92.5% TRE and 50.9% NRE were achieved after 600 s. A modified kinetic model on TRE and NRE considering the induction time was developed and accurately correlated the experimental results. A significant co-oxidation effect of methanol and landfill leachate in SCWO was detected. Furthermore, heterogeneous catalysts were added to SCWO of landfill leachate to improve the removal rate of organic contaminants. A series of composite catalysts (CeMnOx/TiO2) which consisted of the cerium, manganese and titanium oxides were prepared by impregnation method with varying Ce/Mn ratio. Compared with the SCWO of leachate without catalyst, the CeMnOx/TiO2 catalyst with Ce/Mn ratio of 1:2 exhibited high catalytic activity and stability. Additionally, a catalytic reaction mechanism was proposed. It was assumed that MnOx is the active component and CeO2 is the additive and oxygen supplier. The results obtained from this work suggest the SCWO with high-efficiency and stable catalyst could be a promising technology for landfill leachate treatment.

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