Investigation on the humification of municipal solid waste incineration residue and its effect on the leaching behavior of dioxins

In this study, we investigated the humification of municipal solid waste incineration residue through identification of extracted humic substances, and examined the leachability of dioxins by batch leaching test. The samples were incineration residues excavated from lysimeters 6–8 years after being filled. The results of investigation of humic substances showed that the top layers from the surface to a depth of 30–70 cm contained more humic substances than the other layers judging from the color of the samples and optical characteristics of the extracts. In particular, humification in the lysimeter filled with a small amount of compost had progressed through all the layers, not only the top one. The tests revealed that the leaching concentrations of dioxins increased with advanced humification and showed relatively good correlation to dissolved organic carbon (DOC) of leachate at each lysimeter. Humification advances from the surface first, and DOC generated from the humification may preferentially carry down the highly chlorinated dioxin compounds such as O8CDD as DOC–dioxin complexes. Comparing the content and leaching concentration according to depth, we observed not only a decrease in dioxin content but also an increase in leaching of the highly chlorinated dioxins at deeper layers in the lysimeters with the compost. This tendency seemed to result from biological activities.