ANALYSIS OF THE DIFFERENCES BETWEEN ACTUAL DATA AND USEPA, UNFCCC AND IPCC METHODOLOGIES FOR ESTIMATING LANDFILL CH4 GENERATION POTENTIAL

摘要

Waste disposal is a major concern in many countries and landfills are an option for undeveloped nations without resources for other methods of treatment. The main global impact of landfills is the methane produced from anaerobic digestion, which has a significant effect in global warming, if released to the atmosphere. The economic use of this biogas is possible, but for a better evaluation, a strong methodology to estimate the methane generation potential is necessary. There are many estimation methods developed by different organizations and this study will focus on USEPA (United States Environmental Protection Agency), UNFCCC (United Nations Framework Convention on Climate Change) and IPCC (Intergovernmental Panel on Climate Change) methodologies. A large sanitary landfill in Brazil is measuring its methane generation in order to achieve carbon credits according to the Kyoto Protocol since 2008. These measurements along eight years were compared to the values predicted by the methods cited above and very different results were revealed for the three methodologies. The USEPA was the worse result overestimating the methane amount in 27.57%, while the UNFCCC method resulted an average value 14.71% smaller than measured. The IPCC methodology prove to give good results with a value only 5.18% greater than measured. The main difference is that the IPCC method takes in account more details from the waste composition and uses a better calculation of the decay constant, ensuring a better representation of the process. The company has used this analysis to install biogas driven engines and is actually generating 8.2 MW of electricity. The prediction is that there will be methane enough to run the engines up to the year of 2039, considering IPCC estimations. USEPA and UNFCCC results indicate methane generation up to 2089 and 2056 respectively. Predictions very different from reality may lead to wrong sizing and determine the failure of the project.