Supercritical water oxidation of MSW leachate: Factor analysis and behavior of heavy metals

Abstract

Generated from municipal solid waste (MSW) landfill sites and incineration plants, leachate may contain various contaminants such as ammonia, organic pollutants and heavy metals; thus it is difficult to be treated by conventional methods. In this work, supercritical water oxidation (SCWO) of leachate was conducted in a batch reactor based on orthogonal test. The effect of operation parameters on the destruction of organics and the removal of heavy metals was examined. Range and variance analysis revealed that, factors that affected chemical oxygen demand (COD) destruction, in descending order, are oxygen, temperature, reaction time and pressure; for ammonia nitrogen (NH4‐N), the order was temperature, oxygen, reaction time and pressure. It was proven that pressure at supercritical region had limited influence on oxidation reaction. Destruction efficiencies of COD and NH4‐N increased significantly with rising temperature and oxidant amount, with a maximum value of 98.5 and 76.2% for COD and NH4‐N, respectively. Besides, a large proportion of heavy metals in original leachate precipitated into solid ash. Energy dispersive spectroscopy analysis indicated that the main component of solid product was calcium carbonate; metal elements accounted for 35 wt % of the ash. Furthermore, submicron crystalline hydroxyl‐Fe oxide detected by X‐ray diffraction spectra was considered to be formed through complicated process including decomposition and oxidation. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1117–1124, 2014