Abstract
For quantitative estimation of the intra-layer porous structure in the initial stage of landfill formation with municipal solid waste incineration (MSWI) bottom ash, the water absorption of individual MSWI bottom ash particles was measured under still-water, degassed, and agitated conditions. The ratio of the water absorption rate found for the still-water procedure to the effective absorption capacity which was the one under degassing was 35.2%. In the water flow experiment of a column filled with MSWI bottom ash, the true density of the bottom ash was higher after water flow than before, which indicated that dissolution of the soluble components of the bottom ash particle surfaces resulted in a loss of apparent particle volume that more than offset the accompanying weight loss. The volume-based water absorption rate found for the bottom ash particles following 50 mL/h water flow through the column, as a ratio to the effective absorption capacity was about 51.8% of the effective absorption capacity. In a landfill layer comprised of MSWI bottom ash, it was suggested that some regions of the ash particle interiors underwent almost no contact with water.
Highlights
In Japan, approximately 80% of municipal solid waste is incinerated and its importance is growing, as finding new sites for final disposal has become more and more difficult, in urban areas
In the water flow experiment of a column filled with municipal solid waste incineration (MSWI) bottom ash, the true density of the bottom ash was higher after water flow than before, which indicated that dissolution of the soluble components of the bottom ash particle surfaces resulted in a loss of apparent particle volume that more than offset the accompanying weight loss
The ratio of the water absorption rate found for the stillwater procedure to the effective absorption capacity was 35.2% in the weightbased, which was the lowest found in any of the procedures and showed that only about 1/3 of the effective absorption capacity was utilized in still-water
Summary
In Japan, approximately 80% of municipal solid waste is incinerated and its importance is growing, as finding new sites for final disposal has become more and more difficult, in urban areas. Incineration residues are high in calcium (Ca) content and may be expected to undergo mineralization and changes in physical microstructure, with carbonation by carbon dioxide (CO2) generating mainly such minerals as calcite (CaCO3), ettringite (3CaOAl2O3CaSO4·32H2O), gypsum (CaSO4·2H2O), and anhydrite (CaSO4) [6]-[11] These changes are known to result in the gradual formation of water pathways within the landfill layer [12] [13] [14]. Rosqvist and Destouni performed tracer experiments in undisturbed landfill waste samples and showed that approximately 55% - 70% of the infiltrating water followed preferential flow paths [15] This tends to prevent homogeneous washing of landfilled waste components by rainwater and hinders external release of gases generated within the landfill layer [16]
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