Leachate drainage volume of municipal solid waste landfills: field testing and hydro-mechanical modeling.

The leachate drainage volume (LDV) of municipal solid waste (MSW) landfills is crucial to the operation of leachate treatment plant and development at the leachate level, but there is still a lack of reasonable evaluation methods. In this study, the evaluation methods, including both field measurements and numerical simulations, are proposed and applied in the case study of a MSW landfill in Southeastern China. For field measurements, 23 boreholes were drilled to test the leachate level distribution, and thus to determine the saturated volume (SV) of the landfill. The water retention capacity of the drilled samples was tested in a compression cell for a calculation of the undrainage volume (UV) of the landfill, and total LDV was obtained as SV-UV. The total LDV and SV were measured to be 2.31 × 105 m3 and 1.08 × 106 m3, respectively, which indicated a total leachate drainage percentage (LDV/SV) of 22%. For numerical simulations, a hydro-mechanical model is established to predict the daily LDV during layered landfilling. The model couples leachate flow and MSW compression, which are two fundamental processes determining daily LDV. As the model takes into account the leachate generation caused by the compression of MSW, the prediction has a good agreement with the measurement. If ignoring compression, the daily LDV will be underestimated by a percentage of 35%-50%. This study provides basic information and an assessment framework of leachate drainage volume and contributes to leachate management in landfills.

Full-scale experimental study of methane emission in a loess-gravel capillary barrier cover under different seasons.

The methane emission in a loess-gravel capillary barrier cover (CBC) in winter and summer was investigated by constructing a full-scale testing facility (20 m × 30 m) with a slope angle of 14.5° at a landfill in Xi'an, China. Weather conditions, methane emission, gas concentration, temperature, and volumetric water content (VWC) in the CBC were measured. The temperature and moisture in the CBC showed a typical seasonal pattern of warm and dry in summer and cold and wet in winter. Accordingly, the maximum methane oxidation rate and methane emission were higher in summer. The mean methane influx and methane emission decreased significantly as the VWC increased beyond 40% (i.e., a degree of saturation 0.85) at a depth of 0.85 m, which was near the loess/gravel interface. At this depth, more water was presented in the loess layer in the downslope direction due to capillary barrier effects, which increased the upslope methane emission. More dominant methane emission in the middle- and upper-section of the CBC occurred in summer than in winter as there was less soil moisture to facilitate methane transfer. The LFG balance showed that a significant fraction of the loaded LFG was not accounted in the flux chamber measurements due to the preferential flow along the edges of the CBC. The maximum methane oxidation rate was 93.3 g CH4 m-2 d-1, indicating the loess-gravel CBC could mitigate methane emissions after landfill closure.