| 英文摘要: | Landfill disposal of municipal solid waste represents one of the largest anthropogenic global methane emission sources1, and recent policy approaches have targeted significant reductions of these emissions to combat climate change in the US (ref. 2). The efficacy of active gas collection systems in the US was examined by analysing performance data, including fire occurrence, from more than 850 landfills. A generalized linear model showed that the operating status of a landfill—open and actively receiving waste or closed—was the most significant predictor of collection system performance. Gas collection systems at closed landfills were statistically significantly more efficient (p < 0.001) and on average 17 percentage points more efficient than those at open landfills, but open landfills were found to represent 91% of all landfill methane emissions. These results demonstrate the clear need to target open landfills to achieve significant near-term methane emission reductions. This observation is underscored by landfill disposal rates in the US significantly exceeding previously reported national estimates, with this study reporting 262 million tonnes in the year 2012 compared with 122 million tonnes in 2012 as estimated by the US Environmental Protection Agency3. The decomposition of municipal waste in landfills is recognized as one of the largest sources of global anthropogenic methane emissions1. Landfills represent the third-largest anthropogenic source of methane in the US, comprising approximately 18% of domestic emissions4. As such, the capture and combustion of landfill methane has been identified as a critical and viable near-term strategy for greenhouse gas (GHG) reductions associated with the waste sector5 in light of the cost and complexity of implementing wide-scale recycling and waste reduction efforts5. This is a particularly relevant strategy in lower- and lower–middle-income developing nations where waste generation is expected to increase 185% and 158%, respectively, over current rates by 2025 (ref. 6). Although the US and many EU nations have required active landfill gas (LFG) capture for more than a decade7, 8, extensive data demonstrating the efficacy of these systems are limited. To fill this important gap, a new data set with more than 1,200 municipal solid waste landfills, both open and closed, resulting from the recently promulgated US GHG Reporting Rule9, 10 was analysed. The GHG reporting program requires municipal landfills that emit more than 25,000 tonnes of carbon dioxide equivalents to electronically report a substantial amount of operating data to the US Environmental Protection Agency (US EPA) annually, including: measured waste acceptance rates, locational data, projected disposal lifetime, and operational data for active gas collection systems (for example, total operational hours, collected methane content)11, if present. In addition, the GHG reporting rule sets out uniform procedures stipulating how sites must collect, validate and report these data. Our analysis of this data set revealed that the total amount of municipal waste disposed of in the US was 262 million tonnes in 2012, 115% greater than the US EPA disposal estimate for the year 2012 (122 million tonnes) that used a materials flow analysis (top-down) approach3 and exceeds the World Bank’s projected municipal waste generation rate for the US in 2025 (ref. 6) of 256 million tonnes by about 4% (Fig. 1). Previously published survey estimates suggested that the US EPA disposal estimate was low12, but the facility-level nature of our estimate combined with the embedded quality assurance checks makes our estimate the most accurate for the US so far. As our estimate captures disposal at facilities subject to the GHG Reporting Rule, the quantities in Fig. 1 are likely to be underestimates because smaller landfills are not required to report. We estimated that an additional 10 million to 36 million tonnes of waste were disposed of in 2011 (see Supplementary Information). The differences in our estimate from the published top-down estimates are likely to stem from errors introduced in top-down methods associated with assumptions regarding waste generation factors for different economic indicators.
| http://www.nature.com/nclimate/journal/v6/n2/full/nclimate2804.html
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