Optimized Landfill Biocover for CH4 Oxidation II: Implications of Spatially Heterogeneous Fluxes for Monitoring and Emission Prediction

Abstract

Landfill emission monitoring is a prerequisite for the assessment of the efficiency of methane oxidation systems. Monitoring methods have limitations related to the spatial representativeness in small scale methods such as chambers, and separability of emission sources for large scale measurements. In the present study, the reliability of the chamber method was combined with the requirement of spatial representativeness using a novel large scale chamber with a base area of 17.6 m2. The emission for the entire test cell was used as a baseline to test spatial representativeness of the widely used monitoring technique of surface FID screening. Even on the scale of the investigated 953 m2 test cell the variability of emissions was so high that the number of measurements required to capture the total emission would not have been feasible with chambers of conventional size. The main part of emissions occurred upslope. This was attributed to the capillary barrier, which served both the reduction of leachate infiltration and the spatial harmonization of the landfill gas load in the capillary block. A campaign-specific correlation was observed between surface methane concentrations and actual emissions. However, the error of the slope and intercept of the data fit produced an overall error of 94% for emissions predicted from surface concentrations in the same campaign. Moreover, the nature of the correlation changed from campaign to campaign, reflecting the changing specific combination of environmental conditions on the very measurement day, so that a generalized relationship between surface concentrations and fluxes could not be established. Keywords: Biocover, capillary barrier, emission monitoring, flux chamber, landfill, methane oxidation.