Evaluation of pre-treatment methods for landfill disposal of residues from municipal solid waste incineration.

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This study was based on the investigation of Pb, Cd, Ca, and Cl in one individual batch of bottom ash and fly ash (mixture 5:1) resulting from a specific municipal solid waste incinerator (MSWI) in Japan. This mixture ash was stabilized as the following pretreatments: water washing, carbonation, and phosphate stabilization. After the optimum processing condition for each pretreatment was determined, the performance of each pretreatment was examined using pH stat leaching tests (pH 6, 9, 12) and availability tests. For the performance tests, fly ash alone was used, instead of a mixture of MSWI residues, to observe leaching differences among the pretreatments more distinctly. Water washing effectively removed the major elements from MSWI residues and also reduced the leachability of trace metals, such as Pb and Cd, from MSWI residues. A washing time of 15 min with an L/S ratio of 5 was reasonably effective. Carbonation had a significant effect on leachability in alkaline ranges (pH 9 and 12), due to carbonation only on the surface of MSWI residues, not in the center matrix. A moisture content of 10-16.7% appeared to be suitable for carbonation. Phosphate stabilization, even with small doses of phosphate (0.16 mol-PO4^3- kg^-1 sample), was very effective at reducing the leachability of heavy metals.
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