An Assessment of the Dynamic Global Warming Impact Associated with Long-Term Emissions from Landfills

Abstract

Landfills are a major contributor of anthropogenic CH 4 emissions. Since the greenhouse gas (GHG) emissions associated with landfilling waste can occur over decades to centuries, the standard static approach to estimating global warming impacts may not accurately represent the global warming impacts of landfills. The objective of this study is to assess the implications of using 100 yr and 20 yr static and dynamic global warming potential (GWP) approaches to estimate the global warming impacts from municipal solid waste landfills. A life-cycle model was developed to estimate GHG emissions for three gas treatment cases (passive venting, flare, CH 4 conversion to electricity) and four decay rates. For the 100 yr GWP, other model uncertainties (e.g., static GWP values, decay rate, moisture content, or gas collection efficiency) generally had a larger effect on the estimated global warming impact than the choice of static versus dynamic GWP methods. This shows that when comparing single-point GWP values, the choice of static versus dynamic is relatively unimportant for most landfills. While dynamic GWPs consider temporal variance and provide useful estimates for the warming over a set time horizon, for most comparative analyses, static values provide reasonable bounds for the actual 100 yr warming impact.

Development of Streamlined Life-Cycle Assessment for the Solid Waste Management System

“…When recyclable materials are source-separated, recycling efficiencies are dominant such that increasing recycling rate, particularly of old corrugated containers (OCCs), substantially reduces the impact on the ecotoxicity and the human health noncancer effect by avoiding aqueous zinc emissions from the primary production of recyclable materials. For climate change mitigation, the results show that landfill gas collection and oxidation efficiencies, as well as the moisture content of vegetable food waste, are the major contributors to uncertainty in the global warming potential since they substantially affect methane yield and emissions and carbon storage in landfills . Eutrophication is strongly influenced by the electricity conversion efficiency of the engines used for converting landfill gas to electricity due to avoided emissions of phosphate from electricity substitution.…”

“…Even though global warming potentials are reported in a majority of MSWM LCA studies, ,,,− they do not necessarily provide a representative estimate for total human health and environmental impacts since climate change contributed less than 10% to the overall environmental burden (Figure ). Nonetheless, Figure shows that the GHG-only LCA consistently selected the same three scenarios that lead to the lowest environmental burdens as the full and streamlined LCAs.…”

“…To provide estimates of the overall impacts including the input uncertainty, 143 input parameters were varied, including material properties (e.g., moisture content and metal content of each component) and unit process coefficients (e.g., landfill gas collection and oxidation efficiency). These inputs were chosen because they have been shown to result in large uncertainties in the impact estimates of MSWM systems. ,,− Their default values and distributions are summarized in Table S4. To explore the comparative results between the streamlined and full LCAs in consideration of input data uncertainty and inclusion of specific impact categories, a 10 000 iteration Monte Carlo analysis was performed considering the selected 143 uncertain inputs simultaneously for each of 18 scenarios.…”

“…The GHG-only LCA was built only considering the relevant greenhouse gas emissions (i.e., carbon dioxide [CO 2 ], methane [CH 4 ], carbon monoxide [CO], and nitrous oxides [N 2 O]) and the subsequent global warming potentials. Moreover, many waste LCAs only consider climate change because the emissions and their characterization are relatively well established compared to other impact categories. ,,− However, assessing climate change alone may risk problem-shifting to other toxicity-related impacts since global warming is not well correlated with toxic emissions . These findings highlight that global warming is not necessarily a representative metric for the overall environmental burden in processes where toxic substance emissions are important.…”

“…For climate change mitigation, the results show that landfill gas collection and oxidation efficiencies, as well as the moisture content of vegetable food waste, are the major contributors to uncertainty in the global warming potential since they substantially affect methane yield and emissions and carbon storage in landfills. 38 Eutrophication is strongly influenced by the electricity conversion efficiency of the engines used for converting landfill gas to electricity due to avoided emissions of phosphate from electricity substitution.…”