Fates and partitioning of heavy metals in municipal solid waste incineration process

Due to its high population density and rapid increase in per capita waste generation, Taiwan has to adopt incineration technology for treating its municipal solid wastes (MSW). However, the potential emission of heavy metals from MSW incinerators into the environment may pose serious threats on human health and ecology. This issue has not been properly addressed and has caused more public concerns in Taiwan. In this study, the fate the partitioning of heavy metals (including Hg, Cd, Pb, Cr, As, Ni, Cu, and Zn) among fly ash, bottom ash and flue gases generated from three MSWI in Taiwan were determined. Stack sampling results indicate that most As and Hg (more than 80%) exists in gas phase while other metals partition differently. Furthermore, the physical properties, such as particle size, surface area, and elemental carbon content of fly ash were also characterized for better understanding of their effects on the leaching potential of heavy metals. Results collected from different incinerators show that the concentration of heavy metals in fly ash is correlated with its specific area, leached chloride, and elemental carbon content. The concentrations of Cd and Zn in bottom ash are significantly higher than the values typically observed in other countries and the causes are unclear at this stage. The leachability of metals in fly ash is closely related to the pH value of TCLP extraction. Leachability of most metals is found to be higher in acidic conditions than alkaline conditions except for Hg, pb, and Cr. Results of this study would provide better information on how to manage heavy metals coming out of typical MSW incinerators in Taiwan.