Gas Diffusivity Based Characterization of Stabilized Solid Waste from Kurunegala Open Dump Disposal Site

Open dumps are complex ecosystems with respect to Greenhouse Gas (GHG) emission which occurs as a consequence of anaerobic decomposition of organic substances typically available in Municipal Solid Waste (MSW). Subsurface soil conditions (e.g. soil texture, structure) and atmospheric boundary conditions (e.g. wind, temperature) are the major key factors which affect the water retention characteristics, gas diffusivity, and hence the subsurface transport of GHGs. In this study, we characterized the stabilized “soil-like” fraction sampled from an open dumpsite located in Kurunegala, Sri Lanka to investigate subsurface landfill gas (CO2) transport behaviour. The MSW, collected at 2.5–5 m depth was screened to separate the stabilized “soil-like” fractions and proportioned into two groups (0–4.75 mm, 4.75–9.5 mm) for the particle-size based characterization. Soil-gas diffusivity (Dp/Do, where Dp and Do are gas diffusion coefficients in soil air and free air, respectively) and soil–water characteristic (SWC) of the stabilized waste were measured and parameterized using existing and modified parametric models. The results revealed that the investigated material exhibited two-region porosity (i.e., inter-aggregate pore region and intra-aggregate pore regions) which, in turn, affected the water retention and gas transport properties. We further experimentally investigated CO2 gas transport originated from a point source buried in medium bench-scale emission tank under the dry condition and the observed subsurface methane profiles were simulated using the multiphase transport simulator TOUGH2-EOS7CA. In addition, potential effects of atmospheric boundary controls, wind (1.5 and 3 ms−1) and temperature (26 and 34 °C), were also examined based on a series of controlled bench-scale experiments using bench-scale emission tank interfaced with a wind tunnel at the dry condition. Results showed the pronounced effects of particle size and wind and, to a lesser degree, of temperature on soil-landfill gas migration.