Influence of capillary barrier effect on biogas distribution at the base of passive methane oxidation biosystems: Parametric study. (May 2017)

• Record Type: Journal Article
• Authors: Ahoughalandari, Bahar; Cabral, Alexandre R.
• Is Part Of: Waste management. Volume 63(2017)
• Page Start: 172
• Page End: 187
• Publication Date: 2017-05
• Subjects: Landfill final covers -- Passive methane oxidation -- Biogas flow behavior -- Capillary barrier effect -- Numerical simulation; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2016.11.026
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: To the authors' knowledge, this is the first parametric study that incorporates unsaturated hydraulic behavior into the design of passive methane oxidation biosystems (PMOBs). This study showed how the upward flow of biogas across the interface of the main layers of PMOBs may become restricted, due to the capillary barrier effect. The ease and the uniformity in distribution of upward flow of biogas were shown to be mainly influenced by the saturated hydraulic conductivity and the pore size distribution of the methane oxidation layer (MOL) material. The slope of the interface intensifies the effect of saturated hydraulic conductivity and pore size distribution. Abstract: The efficiency of methane oxidation in passive methane oxidation biosystems (PMOBs) is influenced by, among other things, the intensity and distribution of the CH4 loading at the base of the methane oxidation layer (MOL). Both the intensity and distribution are affected by the capillary barrier that results from the superposition of the two materials constituting the PMOB, namely the MOL and the gas distribution layer (GDL). The effect of capillary barriers on the unsaturated flow of water has been well documented in the literature. However, its effect on gas flow through PMOBs is still poorly documented. In this study, sets of numerical simulations were performed to evaluate the effect of unsaturated hydraulic characteristics of the MOL material on the value and distribution of moisture and hence, the ease and uniformity in the distribution of the upward flow of biogas along the GDL-MOL interface. The unsaturated hydraulic parameters of the materials used to construct the experimental field plot at the St-Nicephore landfill (Quebec, Canada) were adopted to build the reference simulation of the parametric study. The behavior of the upward flow of biogas for this particular material was analyzed based on its gas intrinsic permeability function, which was obtained in the laboratory. The parameters that most influenced the distribution and the ease of biogas flow at the base of the MOL were the saturated hydraulic conductivity and pore size distribution of the MOL material, whose effects were intensified as the slope of the interface increased. The effect of initial dry density was also assessed herein. Selection of the MOL material must be made bearing in mind that these three parameters are key in the effort to prevent unwanted restriction in the upward flow of biogas, which may result in the redirection of biogas towards the top of the slope, leading to high CH4 fluxes (hotspots). In a well-designed PMOB, upward flow of biogas across the GDL-MOL interface is unrestricted and moisture distribution is uniform. This paper tries to show how to obtain this.