Development of methods to improve capture of greenhouse gases from bioreactor landfills

Landfill methane (CH4) is a potent greenhouse gas contributing to global climate change, and therefore, it should be captured to reduce emissions of greenhouse gases. Collected CH4 can also be used as an alternative energy source. To control landfill gas (LFG) emissions, gas collection systems of various designs have been used. However, the efficiency of LFG recovery systems can be problematic, particularly before installation of final landfill covers. In addition, despite the widespread use of LFG collection systems for over two decades, little information about their capture efficiency is available because LFG generation rates usually remain unknown. Therefore, in order to enhance the efficiency of CH4 capture and reduce fugitive emissions, it is critical to improve the design of LFG collection systems, properly determine LFG production rates, and quantify gas flow patterns within landfills. This is particularly important for landfills that are actively operated as bioreactors, since LFG production rates are typically higher due to rapid degradation of organic waste, or landfills with intermediate covers in which gas transport between the atmosphere and the landfill body readily occurs. This study explores methods that can improve operation of bioreactor landfills by reducing CH4 emissions and enhancing CH4 collection efficiency, and that can be used to estimate LFG generation rates and the distribution of gas flow parameters within waste.;This work began with the analysis of an innovative gas collection system -- a near-surface high permeability layer -- for enhancing LFG capture and reducing fugitive CH4 emissions. The high-permeability layer serves as a gas conductive layer uniformly distributing gas pressure, which extends the zone of influence of pumping wells. The gas collection system with a near-surface permeable layer was able to entrap LFG far from the well. The uniform pressure distribution above the permeable layer contributed to minimizing oxygen (O2) intrusion into the landfill and maximizing CH4 oxidation throughout the landfill soil cover, in addition to improving the CH4 capture efficiency and reducing fugitive CH 4 emissions. More importantly, the presence of a permeable layer resulted in near constant collection rates of biogas regardless of variations in heterogeneous landfill conditions, such as waste permeability. The near-surface permeable layer also reduced preferential gas flows through cracks in the cover material, resulting in minimal impact of surface cracking on CH4 emissions and O2 intrusion.;A second task was to investigate and advance the baro-pneumatic method, which is used to quantify CH4 generation rates and estimate the gas permeability field. The baro-pneumatic method was modified by incorporating an inverse modeling approach, the pilot point method, to improve the efficacy of the method in landfills with heterogeneous gas permeabilities. Based on synthetic exercises, the inverse model reproduced the spatial permeability distribution reasonably well using transient pressure changes in response to the withdrawal of LFG during pumping tests. The LFG production rate was also successfully estimated using data from baro-pneumatic tests. The LFG flow models were calibrated to the site-specific gas pressure data using the modified baro-pneumatic method. These models were able to provide excellent predictions of gas pressure distributions and flow patterns in heterogeneous landfills.