Characterizing preferential flow in landfilled municipal solid waste

Abstract

Municipal solid waste (MSW) is a porous medium comprising macropores and matrix, such that the flow pattern often takes the form of preferential flow. The objective of this paper was to study the preferential flow in MSW and to quantify the flow character. Dye tracing tests and solute breakthrough tests were carried out using MSW samples taken from different depths of a landfill. Test procedures were proposed to make the sectioning of MSW sample easy. The MSW columns were dyed and then sectioned in the horizontal and vertical direction. Digital image processing technology was used to investigate the preferential flow pattern. In order to quantitatively characterize the preferential flow in MSW, regression analysis was performed on the breakthrough curves using the bimodal probability density model. The dye tracing tests show that more preferential flow happened under a higher application rate, under higher initial water content, and in shallow MSW. The results of vertical sectioning tests are consistent with that of horizontal sectioning tests, showing that the test procedure has no obvious influence on the preferential flow pattern in MSW. The results of the solute breakthrough tests show that between 55 and 70% of the total solute was transported through large pores. The modeled proportion of solute movement through large pores decreases as the depth and age increase, and increases as the application rate increases. The results are beneficial to simulate water and solute migration in MSW using a dual-porosity model.