Spatial Variability in Methane Generation and Methane Oxidation Potential of Excavated Waste Residue: Implications for Landfill Gas Modeling and Waste Valorization

Landfill gas (LFG) models traditionally assume homogeneous waste degradation using a single set of parameters—such as the first-order rate constant (k) and methane potential (L0)—to predict methane (CH4) generation. However, this study demonstrates that waste degradation is highly heterogeneous, with significant spatial variability in CH4 generation and oxidation potential. We investigated the biochemical methane potential (BMP) and methane oxidation potential (MOP) of excavated waste residue (EWR) from different depths within the Calgary Biocell, a landfill bioreactor operated for 14 years with leachate recirculation. Using a modified BMP assay, 12 batch experiments—including 3 composite replicates, 8 grab samples, and 1 blank—were conducted. Results revealed that deeper regions of the Biocell exhibited greater waste degradation, with EWR samples from these zones showing an average L0 of 8.28 mL CH4/g TS, significantly lower than the 18.21 mL CH4/g TS observed in shallower regions. Additionally, EWR samples with higher proportions of paper and cardboard produced greater methane potential. Methane oxidation potential was also depth-dependent, with EWR from deeper regions showing a 62% higher maximum CH4 oxidation rate (Vmax = 0.76 μmol/h) compared to shallower regions (Vmax = 0.47 μmol/h/g). These findings challenge the assumption of homogeneous waste degradation in landfills and highlight the need for spatially resolved models to accurately predict CH4 generation and recovery. The study also underscores the potential for valorizing EWR in landfill biocovers and other sustainable waste management applications.