An Experimental and Analytical Approach to Understanding the Dynamic Leaching from Municipal Solid Waste Combustion Residue

Abstract

This paper describes an experimental technique involving the use of small columns for generating significant quantities of leachate data from municipal solid waste (MSW) solid residues within a relatively short amount of time. Data analysis using the discretized mass balance equations descriptive of the system results in best estimates of governing transport parameters that can, in turn, be used to predict the long-term release of leachable components (As, Cd, Cu, Fe, Ni, Pb, Zn, Ca, Mg, Na, K, Cl, SO 4) from the solid matrix. Results indicate that both chemical solubility and physical transport are important factors affecting the flux of contaminants from the solid to the solution phase.

A consistent geochemical modelling approach for the leaching and reactive transport of major and trace elements in MSWI bottom ash

“…However, if it is assumed that the stagnant zones consist of micropores within spheres with a radius of 2 mm (i.e., the largest particle size fraction in the sample), an effective diffusion coefficient (D e ) in the order of 10 À12 -10 À13 m 2 /s is found (for details of this calculation see Appelo and Postma, 2005). This value is similar to that found by Gardner et al (2002) for the leaching of conservative elements (Na and Cl) from MSWI fly ash columns.…”

“…The consistent ''multi-surface" reactive transport modelling approach presented in this study leads to a strongly improved model prediction and understanding compared to previous reactive transport modelling studies performed on MSWI bottom ash (e.g., Bäverman et al, 1997;Yan et al, 1999;Dijkstra et al, 2002;Baranger et al, 2002;Gardner et al, 2002). Novel aspects of the present modelling approach include the characterization of DOC in terms of its reactive components HA and FA as a function of L/S and pH, the inclusion of mechanistic models that predict the binding of metals to these substances, the inclusion of a surface complexation model that predicts FA concentrations, and finally, the combination of these geochemical models with non-equilibrium processes.…”

“…To predict MSWI bottom ash leaching in a percolation regime, the geochemical part of the model was extended with one-dimensional transport of water. To account for physical non-equilibrium (e.g., as indicated by observed ''tailing" of element concentrations by Dijkstra et al, 2002;Gardner et al, 2002) the ''dual porosity" approach (e.g., Toride et al, 1999) was followed. The dual porosity approach assumes that the liquid phase is partitioned in a mobile (flowing) and immobile (stagnant) zone.…”

“…The material is known for its complex physicochemical characteristics and metastable mineralogical composition Chandler et al, 1997) and is considerably enriched in potentially toxic trace elements compared to its parent material (Chandler et al, 1997). Although geochemical models have been used successfully to identify the leaching processes in MSWI bottom ash in batch experiments (e.g., Johnson et al, 1996;Comans, 1997, 1999;Dijkstra et al, 2006a), reports on the application of such models to dynamic MSWI bottom ash systems are, however, relatively scarce (Bäverman et al, 1997;Dijkstra et al, 2002;Baranger et al, 2002;Gardner et al, 2002;Mostbauer and Lechner, 2006). Dijkstra et al (2002) used a reactive transport model based on equilibrium chemistry to identify processes that control the leaching of major and trace elements from weathered MSWI bottom ash in a percolation test.…”

Probabilistic Modeling of One-Dimensional Water Movement and Leaching from Highway Embankments Containing Secondary Materials

“…Some researchers have modeled the pH-dependent leaching behavior by equilibrium dissolution/precipitation reactions (Kida et al, 1996;Fallman, 2000), and more recently by sorption reactions (surface complexation and surface precipitation) (Meima and Comans, 1998;Dijkstra et al, 2002). Others have coupled diffusion with chemical equilibrium to model leaching behavior in the laboratory (Ganguly et al, 1998;Gardner et al, 2002;Park and Batchelor, 2002;Kosson et al, 1996Kosson et al, , 2002 suggested use of a percolation and a diffusion equation to extend laboratory results to field leaching conditions. Most of these studies have assumed that the water flow through the secondary material was uniform and constant, and did not consider the unsaturated flow in their analyses.…”