Numerical Analysis of Water and Gas Migration Within a Landfill Biocover Using a Two-Phase Flow Model

Modern engineered landfills are important facilities for the disposal of municipal solid waste (MSW). The biodegradation of organic components of MSW under anaerobic conditions produces biogas (55-60% methane and 40-45% carbon dioxide by volume) which contributes to climate change. Biocover systems are recently developed innovative and cost-effective solutions to reduce CH4 emission from MSW landfills based on microbial CH4 oxidation in landfill covers. A biocover is comprised of two components: (a) a methane oxidation layer (MOL) and (b) an underlying gas distribution layer (GDL). This paper examines the performance of a biocover with a zig-zag shaped MOL-GDL interface using a two-phase flow model. Results demonstrate that the length of unrestricted gas migration (LUGM) is sensitive to the selected threshold volumetric gas content (theta(a,occ)) as occlusion to gas migration. When selecting the theta(a,occ) value from the gas permeability function of the MOL material, a slight difference of theta(a,occ) (less than 0.04) may yield different outcomes regarding the performance of biocovers. The numerical modelling also indicates that the use of the LUGM without considering gas flow rates across the MOL-GDL interface seems unlikely suitable as the design criterion for biocovers to minimize hotspot formation.