Elements of Design of Passive Methane Oxidation Biosystems: Fundamental and Practical Considerations About Compaction and Hydraulic Characteristics on Biogas Migration

Passive methane oxidation biosystems (PMOBs) are often proposed as a means to reduce fugitive landfill CH₄ emissions, i.e. emissions not captured by gas collection systems. However, current designs may lead to the formation of a capillary barrier along the interface between the two main layers constituting passive biosystems, namely the methane oxidation layer and gas distribution layer. The formation of a capillary barrier may result in restricted upward flow of biogas at the base of methane oxidation layer, thereby leading to concentrated biogas emissions in regions known as hotpots, where passive oxidation of biotic methane is failing, if not absent. In this study, design criteria are introduced to assess the ease of biogas flow across the gas distribution-methane oxidation layers’ interface. Laboratory experiments were conducted to obtain the water retention curve, air permeability function and line of optima (on Standard Proctor curve) of the materials used to construct the methane oxidation layer of two experimental PMOBs at the St-Nicephore (Quebec, Canada) landfill. In addition, the main characteristics for other materials were obtained from the literature. Design criteria were then defined based on the degree of water saturation at the lines of optima and the pattern of air permeability functions and water retention curves. Considering these criteria in the design of PMOBs is fundamental to reduce the risk of creating hotspots when implementing PMOBs.