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Landfill gas analysis to support an assessment of organic waste stability




Mantell, Steven C., author
Bareither, Christopher A., advisor
von Fischer, Joe C., committee member
Sharvelle, Sybil E., committee member

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Organic stability is defined as the state of near complete decomposition of organic waste constituents such that human health, environmental, and financial risks associated with undecomposed waste are reduced. An assessment of organic stability was completed based on comparison between collected and predicted landfill gas. There were two main objectives of the study: (i) assess landfill organic stability for an entire site and specific landfill phases to evaluate how operational practices influence organic stability and (ii) develop recommendations for conducting organic stability assessments based on gas collection and modeling. Landfill gas generation is frequently assessed on a site-wide basis; however, the process of waste disposal and subsequent gas generation varies temporally and spatially within a landfill. In this study, landfill gas modeling was conducted on a site-wide and phase-specific basis (i.e., multiple phases constitute the entire landfill site) for a non-hazardous solid waste landfill in the U.S. The U.S. EPA's LandGEM model for methane generation was used for the gas model simulations. LandGEM calculates the rate of methane generation based on the mass of solid waste, methane generation potential of the waste, and first-order rate coefficient (k). Models were completed that considered the following factors: (i) constant methane generation potential; (ii) methane flow rates representative of monthly and annual averages; (iii) collection efficiency of the landfill gas collection system; and (iv) optimization of k to reduce the sum of squared residuals between measured and predicted methane flow rates. Collection efficiency of the landfill gas collection system was accounted for in the models via assuming a constant collection efficiency of 85% and assuming a temporally varying collection efficiency. The temporally varying collection efficiency was used to represent temporal installation of a gas collection system and placement of interim and final cover. Site-wide decay rates varied from 0.068 to 0.070 1/yr while phase-specific rates varied from 0.021 to 0.12 1/yr. Observations reinforce previous studies showing that moisture enhancement has potential to create favorable landfill conditions that may lead to higher rates of methane generation and shorter durations to achieve organic stability.


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municipal solid waste
gas modeling
organic stability


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