Validation of Capturing Landfill Emissions for Energy Needs (CLEEN) model

With the threat of climate change upon us and with the tightening supplies of fossil energy resources, we find that our current system cannot be sustained indefinitely. Under these circumstances, we are faced with the challenge of developing renewable energy resources. Daily, there are millions of tons of municipal solid waste deposited into thousands of landfills and other dumping sites worldwide. The decomposition of organic material anaerobically in landfills results in the production of methane, which can be burned as an alternative fuel. To assess the amount of methane generated by a landfill, models predicting methane generation are necessary. The most widely-used landfill gas model in the U.S. is the U.S. Environmental Protection Agency's (EPA's) LandGEM. This model, however, has several shortcomings, including the fact that it does not account for the variations in waste composition, rainfall and ambient temperature. To improve our ability to estimate methane generation rates from landfills, UT Arlington (Karanjekar, 2012) has developed the Capturing Landfill Emissions for Energy Needs (CLEEN) model, which allows methane generation to be estimated for any landfill, with basic information about waste composition, annual rainfall, and ambient temperature.;The objectives of this research were to find a scale up factor for the methane generation rate-constant (needed because laboratory methane generation rates exceed field rates), to validate the CLEEN model by comparing its predictions with field data, and to develop a user interface for the model.;To develop the model scale-up factor, 5 data sets of waste tonnage and methane recovery data were obtained from consultants for 3 landfills in California and 2 in Texas. For each location, average annual ambient temperature and rainfall were obtained for the nearest airport from the National Climatic Data Center. EPA's national waste composition data was used, except for the Denton Landfill, for which waste composition data was available.;The scale-up factor can be defined as the ratio of the actual k value found in the landfill to the k value computed using the CLEEN model comprehensive regression equation. The observed average methane flow rate recovered from each landfill was plotted along with a methane recovery curve computed from the CLEEN model. For each landfill, trial and error was used to determine a kactual value which produced a best-fit of the CLEEN model methane recovery curve to the actual data. The average scale-up factor for the 4 landfills was found to be 0.0083.;CLEEN model validated result for Southern California Landfill 2 was compared with the most commonly used other landfill emission models, EPA's LandGEM and the Intergovernmental Panel on Climate Change (IPCC) model. The CLEEN model with a California specific scale-up factor (based on the other California landfills only) gave predictions that were closest to the actual methane recovered, with an R2 value of 0.79. The CLEEN model with the overall scale-up factor (based on all 4 landfills) predicted methane recovery values second best. All models except CLEEN with the California-specific scale-up factor over-predicted methane recovery. A user interface was created in Matlab for the convenience of users to feed in the data and obtain the estimated methane recovery.