Effect Of Enhanced Leachate Recirculated (ELR) Landfill Operation And Gas Extraction On Greenhouse Gas Emission

Abstract

The bioreactor/ enhanced leachate recirculated (ELR) landfill operation with the addition of moisture/ leachate to the landfill, accelerate the process of landfill waste decomposition; and increase the generation of LFG over a shorter period of time. Since emissions from the landfills are directly related to the gas generation, the increase in gas generation might also increase the emission from the landfill. On the contrary, the presence of gas extraction is suggested to mitigate the fugitive emissions from the landfills. Therefore, the motivation of the current study was to evaluate the effect of ELR operation as well as the gas extraction on the greenhouse gas emissions from the landfill. The current study was conducted in the City of Denton Landfill, Texas. Methane emission was investigated using a portable FID and static flux chamber technique from the landfill surface. Emission was measured from an ELR operated cell (cell 2) as well as a conventional cell (cell 0) in the City of Denton Landfill. Methane emission for cell 2 varied from 9544.3 ppm to 0 ppm while for cell 0, it varied from 0 ppm to 47 ppm. High spatial variations were observed during monitoring from both cells 0 and cell 2 which could be recognized as the variation of gas generation below the cover soil. The comparison between emissions from the slope and surface of the landfill showed that more methane emission occurred from the slopes than the top surface. In addition, the average landfill emission showed an increasing trend with increase in temperature and decreasing trend with increasing precipitation. The effect of ELR operation near the recirculation pipes showed a lag period between the recirculation and the maximum emission near the pipe. The emission near the pipe decreased after 1 day of recirculation and after the initial decrease, the emission started to increase and continued to increase up to 7 days after the recirculation. However, approximately after 10 days of recirculation, the emission resumed its original state before the recirculation. It should be noted that the change in emission was only limited near the pipe. No overall change in emission was observed from the cell due to the recirculation. The comparison between the emissions from the conventional and ELR cell showed an overall higher emission from the ELR cell which could be attributed to the overall higher gas generation from the ELR cell as well. The gas extraction had a direct impact on emission, the emission dropped substantially right after the gas extraction from the landfill. However, the gas was extracted once in a month and comparison with the amount of gas extraction and emission showed that the emission decreased as the gas extraction increased. An attempt was made to incorporate the effect of ELR operation and the gas extraction in the estimating the methane emission from the landfills. Multiple linear regression (MLR) model was developed using the statistical tool SAS. The developed model was validated and the model showed an excellent agreement between the predicted emission and the measured emission from the landfills (average variation 9.6%).