Life cycle GHG emissions of MSW landfilling versus Incineration: Expected outcomes based on US landfill gas collection regulations

From a GHG perspective, most LCA studies find incineration (MSWI) to be preferred over landfilling because of high energy recovery offsets. In some studies, however, landfilling results in less greenhouse gases (GHG) emissions than MSWI. We investigated using LCA, the landfill gas (LFG) collection efficiencies and waste composition that led to landfills resulting in less GHG emissions. Then, we explored what theoretical minimum lifetime gas collection efficiencies can be expected when following US LFG regulations. Only landfills with high LFG collection efficiencies (at least 81%) and recovery of methane for energy resulted in less GHG emissions compared to the management of the same waste stream in MSWI; required efficiency increased to 93% without LFG energy recovery. Expected theoretical lifetime LFG collection efficiencies were modeled in the range of 30-80%, with the lower rates associated with landfills having smaller input masses, high decay rates, and low concentrations of nonmethane organic compounds (C_NMOC). Our modeling found that only under a limited combination of conditions (e.g., high C_NMOC, high waste input rate, low decay rate) could a landfill expect to achieve a LFG collection efficiency as high as 80%, and that this value falls just under the 81-93% collection efficiency threshold needed for a landfill to result in less GHG emissions than MSWI. When exploring the influence of higher oxidation rates, changing decay rates, varying electricity grids, and inclusion of nonferrous metals recovery offsets the collection effciency range needed increased in nearly all cases; the electricity grid and nonferrous metals offsets had the greatest influence.