Analytical Model for Multicomponent Landfill Gas Migration through Four-Layer Landfill Biocover with Capillary Barrier

An analytical model was developed to simulate migration of methane (CH4), oxygen (O2), carbon dioxide (CO2), and nitrogen (N2) through a four-layer landfill biocover, which can account for the four-layer structure and the diffusion-advection-CH4 oxidation processes. The model was effectively validated against experimental data first. The influences of several important factors including pressure difference, degree of saturation, CH4 oxidation, and layer thickness were then investigated. The water accumulating at the capillary layer benefits mitigating CH4 emission. But increasing the degree of saturation of the top layer enhances CH4 emission. The CH4 emission rate is controlled by both diffusion and advection in the top layer but mainly controlled by advection in the capillary layer. The CH4 emission rate reaches its minimum when the top layer thickness is close to that of the aerobic zone. Increasing the capillary-layer thickness can reduce CH4 emission more effectively than increasing the total biocover thickness. A capillary layer with a thickness of 0.55 m can control the CH4 emission rate below 0.45 mol/m2/day under a pressure difference of 500 Pa.