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

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.