Experimental comparison of foam flow and gas flow in municipal solid waste

Abstract

Foam is found to be a special fluid (i.e., gas divided by liquid film) that exists in municipal solid waste (MSW) landfills. As a disconnected phase, the unsaturated flow behavior of foam is significantly different from that of gas in connected phase. In this study, the difference between foam flow and gas flow was characterized through displacement tests in the MSW columns. Resistance factor, which is defined as the ratio of steady pressure drop between foam displacement and gas displacement, is employed to characterize this difference. The effects of foam quality, void ratio, and particle size on resistance factor were studied. The unsaturated permeability curves of foams generated by leachate samples at different depths were measured. The leachate at the middle layer has low surface tension to produce strong foam, while the leachate at the top and bottom layers has high surface tension to produce weak foam. The unsaturated permeabilities of weak foam and strong foam were about 1 and 2 orders of magnitude smaller than that of gas, respectively. The reduction in waste void ratio decreased the resistance factor as the excessive shearing effect in small pores would cause the foam to collapse.