Critical review of the methane generation potential of municipal solid waste

ABSTRACT

The ultimate methane generation potential (L₀) of municipal solid waste (MSW) has been used in first-order decay models for the estimation of landfill gas (LFG) production for the previous 30 years. L₀ is an inherent property of the waste component, often a function of the lignocellulosic concentrations within. Methane yields of individual waste components can be measured in a controlled laboratory setting; however, the extent to which each portion degrades in a landfill is uncertain. Methane generation in a landfill is difficult to estimate due to the spatial and temporal variations among sites and the heterogeneous composition of MSW streams. Predicting LFG production is further complicated by prior aerobic degradation, fugitive gas emissions that escape into the atmosphere, and unforeseen chemical inhibition within the landfill environment. Published L₀ values are reviewed and compared to the methane yields of mixed-waste and waste components measured in the laboratory. Experimentally determined values of mixed MSW ranged from 35 to 167 m³ CH₄/Mg MSW. Modeled values and those based on biodegradability of individual components and waste composition data ranged from 20 to 223 m³ CH₄/Mg MSW. These data constitute a wide range of experimental methodologies and waste composition characteristics with respect to geography and time. The usefulness, comparability, and applicability of such data are discussed. The use of L₀ as a parameter in LFG generation models and life-cycle assessments is reviewed and discussed.

KEYWORDS:

• Landfill
• solid waste
• gas
• methane potential
• modeling

Acknowledgments

The authors would like to thank Dr. Wesley Oehmig, Sarah Gustitus, and Stephanie Bolyard for their comments and suggestions on the first drafts of this critical review. Heijo Scharff gave helpful comments regarding LFG generation models and their parameters. Thanks to Jim Wally at Innovative Waste Consulting Services for providing documentation regarding LCA methane yields. The authors recognize the countless hours researchers, scientists, and engineers have contributed to the increased understanding of methane generation from solid wastes and landfills.