The stable isotope technique is a methodology that allows for the quantification of biologically oxidized methane (CH4) in a landfill cover. In this methodology, the oxidized fraction of methane is calculated based on the isotopic signature of the emitted CH4, the preference degree of methanotrophic bacteria in consuming methane with lighter isotopes and the isotopic signature of methane within anaerobic zone of the landfill. This study was conducted in four separate operational phases of the Vancouver landfill (VLF). These four phases were grouped into two areas based on the characteristics of the soil used as interim and/or final cover. Methane emission rates were measured using a flux chamber technique. The methane samples, which was collected from the landfill’s anaerobic zones, the flux chambers, and aerobic soil incubations test, were analysed for isotopic signature. δ13C values for methane generated in the VLF ranged between -54‰ and -58‰. All CH4 samples collected from flux chambers were enriched in 13C with δ13C values ranging between -35‰ to -56‰. The overall average oxidation fractionation factor (αox) at the VLF was 1.0266 ± 0.0037 at 25 °C. Methane oxidation ranged from 3 to 73% with mean values of 28% and 34% for two different areas of the landfill. Results suggested that the overall methane oxidation percentage, for a region with similar climatic conditions to Vancouver, may be considered more or less constant throughout the year. As our objective was to compare different sections and cover soil types across the landfill, the use of chambers to capture emitted methane was deemed appropriate.
Keywords: Landfill, LFG, methane emission, methanotrophy, methane oxidation, stable isotope.
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