Numerical model for static chamber measurement of multi-component landfill gas emissions and its application

Abstract

The quantitative assessment of landfill gas emissions is essential to assess the performance of the landfill cover and gas collection system. The relative error of the measured surface emission of landfill gas may be induced by the static flux chamber technique. This study aims to quantify effects of the size of the chamber, the insertion depth, pressure differential on the relative errors by using an integrated approach of in situ tests, and numerical modeling. A field experiment study of landfill gas emission is conducted by using a static chamber at one landfill site in Xi’an, Northwest China. Additionally, a two-dimensional axisymmetric numerical model for multi-component gas transport in the soil and the static chamber is developed based on the dusty-gas model (DGM). The proposed model is validated by the field data obtained in this study and a set of experimental data in the literature. The results show that DGM model has a better capacity to predict gas transport under a wider range of permeability compared to Blanc’s method. This is due to the fact that DGM model can explain the interaction among gases (e.g., CH4, CO2, O2, and N2) and the Knudsen diffusion process while these mechanisms are not included in Blanc’s model. Increasing the size and the insertion depth of static chambers can reduce the relative error for the flux of CH4 and CO2. For example, increasing the height of chambers from 0.55 to 1.1 m can decrease relative errors of CH4 and CO2 flux by 17% and 18%, respectively. Moreover, we find that gas emission fluxes for the case with positive pressure differential (∆Pin-out) are greater than that of the case without considering pressure fluctuations. The Monte Carlo method was adopted to carry out the statistical analysis for quantifying the range of relative errors. The agreement of the measured field data and predicted results demonstrated that the proposed model has the capacity to quantify the emission of landfill gas from the landfill cover systems.

Annual fluctuation of gas concentration within the landfill surface layer in a tropical climate: A case study of a municipal wasteyard

“…It is clear that the gas composition of the dump surface layer fluctuated significantly with the annual climatic variations, and the authors previously have proved diurnal gas fluctuations under tropical climatic conditions (Herath, Gunathilake, et al., 2023); it may represent the gas generation and emission changes from landfills. Many previous studies quantified landfill gas emissions throughout the year using mathematical models with or without considering the climatic factor variations (Huang et al., 2022; Ramprasad et al., 2022; Xie et al., 2022). Studying the annual and diurnal fluctuation pattern of landfill gas emission with climatic conditions is a critical factor before quantifying the gas generation or emission, and long‐term studies are required for model development.…”