Removal of organics and ammonia in landfill leachate via catalytic oxypyrolysis over MOF-derived Fe2O3@SiO2-Al2O3

Abstract

Landfill leachate has a severe impact on both human health and ecosystem. To address this matter, we report herein a systematic study of a new oxypyrolysis process composed of cracking-combustion coupled reactions over Fe2O3@SiO2-Al2O3 catalyst for the removal of organics and ammonia in landfill leachate. Fe2O3@SiO2-Al2O3, which contains Brönsted acidity and oxidative sites, is derived from calcination of iron-based MIL-101 nanocast with silica-alumina sol. Fluidized-bed experiments at 339 ℃ reveal the exceptional catalytic activity of Fe2O3@SiO2-Al2O3 as manifested by the high removal efficiency of COD (99.2 %) and NH3-N (95.2 %). The concentration of COD and ammonia nitrogen in the condensed effluent is as low as 18.1 mg/L and 78.9 mg/L respectively, the best performance yet seen in other chemical treatment approaches. The non-condensable gas from the oxypyrolysis reaction only contains CO2, N2 and a trace amount of nonmethane hydrocarbons. Insight into oxypyrolysis reaction is provided by thermogravimetric-gas chromatography/mass spectrometry and in-situ infrared spectroscopy. The amorphous SiO2-Al2O3 enables the catalytic cracking of heavy fractions in landfill leachate to small organic molecules, and the Fe2O3 nanoparticles realize the catalytic combustion of small organic molecules and ammonia to CO2, H2O and N2. A theoretical analysis of the operation cost estimate shows that the oxypyrolysis reaction is among the most cost-effective treatment methods. Taken together, these findings suggest that the oxypyrolysis is highly applicable for the leachate treatment.