This study demonstrates the advantage of the use of stable isotope technique to understand the methanogenic pathways and to quantify the methane production and the rate of production at Trail Road Landfill (TRL) site, Ottawa, Canada. The combination use of leachate water isotopes (2H and 18O) and the concentrations and 13C isotope data of various carbon pools (DOC, DIC, CH4, CO2, acetic acid, propionic acid, humic acid, fulvic acid, and LMW DOC), show that 1) the microbial processes are more advanced in the degradation of DOC in the older part of landfill, and 2) the younger part of landfill shows greater CH4 production (with deuterium excess > 21‰) and methanogenesis is dominated by CO2 reduction, however, the fermentation of accumulated acetate is the dominant methanogenesis pathway in the older landfill. The produced methane was calculated using the isotope mass balance method. For the leachate volume collected at leachate pumping station in 2005 (1.14E+08 L), this would produced about 1.14E + 10 L CH4 (STP), which is very closed to the amount measured at the gas flare station in 2005 (1.11E+10 L).

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