Using observed data to improve estimated methane collection from select U.S. landfills.

Area of Science:

• Environmental Science
• Chemical Engineering
• Geoscience

Background:

• Landfills produce methane, a greenhouse gas and energy source.
• Current U.S. EPA Landfill Gas Emissions Model (LandGEM) uses outdated parameters.
• Accurate methane estimation is crucial for climate and energy assessments.

Purpose of the Study:

• To re-evaluate the first-order decay rate (k) parameter in the LandGEM model.
• To improve the accuracy of methane generation estimates from U.S. landfills.
• To investigate the impact of updated decay rates on early-stage landfill gas production.

Main Methods:

• Collected methane collection data from 11 U.S. landfills.
• Incorporated site-specific gas collection efficiencies.
• Reformulated LandGEM equation and optimized decay rate (k) using formal search techniques.
• Minimized the sum of squared errors between model predictions and observed data.

Main Results:

• Optimal decay rates (k) were consistently higher than the default AP-42 value (0.04 yr⁻¹).
• Weighted average decay rate across landfills ranged from 0.09 to 0.12 yr⁻¹.
• The default LandGEM decay rate is likely underestimated.

Conclusions:

• The default decay rate in LandGEM underestimates methane production, particularly in early landfill years.
• Higher decay rates suggest more methane is generated sooner after waste burial.
• Updated parameters are needed for more accurate landfill methane emission inventories and energy recovery potential.