A steady-state analytical model for coupled methane transport and oxidation in vegetated landfill cover soil

Abstract

The biologically active soils covered by plants are widely applied in landfill final covers for controlling the emission of methane from municipal solid waste. The current study focuses on developing alternative formulations of steady-state analytical modeling for coupled methane transport and oxidation in vegetated landfill cover systems considering the effect of mass exchange via plants’ roots. The proposed analytical frameworks are validated by a set of experimental data. The varied examples of coupled methane transport and oxidation are evaluated by the proposed solution to discuss the effects of the properties of roots and soils on the overall performance of vegetated landfill covers. It was shown that the increment of the root depth or root density can effectively contribute to the reduction of CH4 emission from landfill cover systems while coupled effects of advection/diffusion and oxidation rate may influence the overall performance of CH4 transport. For example, increasing root density from 100 m/m3 to 3 × 103 m/m3 can lead to a reduction of CH4 emission rate by a factor of 1.3. This is mainly attributed to the increase of aerobic zone with the root density growing. It is found that the methane removal efficiency is more sensitive to variations of the saturation outside the root zone (S2) than that in the root zone (S1) as gases inlet fluxes are largely reduced and the role of the plant is weakened for a larger S2. The present analytical models may provide an easy-to-use tool for performance evaluation of cover systems, benchmark studies, parameter identification and sensitivity analysis.