First-order kinetic gas generation model parameters for wet landfills

Landfill gas collection data from wet landfill cells were analyzed and first-order gas generation model parameters were estimated for the US EPA landfill gas emissions model (LandGEM). Parameters were determined through statistical comparison of predicted and actual gas collection. The US EPA LandGEM model appeared to fit the data well, provided it is preceded by a lag phase, which on average was 1.5 years. The first-order reaction rate constant, k, and the methane generation potential, Lo, were estimated for a set of landfills with short-term waste placement and long-term gas collection data. Mean and 95% confidence parameter estimates for these data sets were found using mixed-effects model regression followed by bootstrap analysis. The mean values for the specific methane volume produced during the lag phase (Vsto), Lo, and k were 33 m3/Megagrams (Mg), 76 m3/Mg, and 0.28 year−1, respectively. Parameters were also estimated for three full scale wet landfills where waste was placed over many years. The k and Lo estimated for these landfills were 0.21 year−1, 115 m3/Mg, 0.11 year−1, 95 m3/Mg, and 0.12 year−1 and 87 m3/Mg, respectively. A group of data points from wet landfills cells with short-term data were also analyzed. A conservative set of parameter estimates was suggested based on the upper 95% confidence interval parameters as a k of 0.3 year−1 and a Lo of 100 m3/Mg if design is optimized and the lag is minimized.