Leaching Behaviour of Elements and Evaluation of Pre-treatment Methods for Municipal Solid Waste Incinerator (MSWI) Residues in Column Leaching Tests

Two new pre-treatment methods (water-washing/carbonation and carbonation/phosphate stabilisation) of municipal solid waste (MSW) incinerator residues were evaluated by column leaching tests under aerobic conditions and anaerobic conditions (which were changed to aerobic conditions after 10 months). A mixture of bottom ash and fly ash (5:1 ratio) was pre-treated using each method. Shredded incombustible residues (SIR) were added to each ash preparation in proportions similar to the ratios present in landfills. For comparison, landfill wastes typical of Japan, i.e., a mixture of bottom ash, chelating-pre-treated fly ash, and SIR, were also examined. Leachate samples were collected periodically and analysed over a 15-month period. When compared to chelating pre-treatment, both water-washing/carbonation and carbonation/phosphate stabilisation reduced the leaching of Pb, Al, and Cu by about 1-2 orders of magnitude. Moreover, the initial concentrations of Ca and Pb in leachates from column of water-washing/carbonation were 56-57% and 84-96% less than those from column of carbonation/phosphate stabilisation. Therefore, water-washing/carbonation was considered to be a promising approach to obtain early waste stabilisation and to reduce the release of heavy metals to near-negligible levels. The leaching behaviour of elements was also discussed.