According to the study, 262 million tons of municipal solid waste were disposed of in the United States in 2012. That’s a 115% increase over the U.S. Environmental Protection Agency’s (EPA) estimate of 122 million tons for the same year. The new estimate also surpasses the World Bank’s projections of municipal solid waste generation for 2025.
A key difference is in the methodology, said Jon Powell, a Ph.D. student in Yale’s Department of Chemical & Environmental Engineering and lead author of the paper. The EPA has traditionally published waste generation and disposal figures using a “materials flow analysis” method, based on information from industry associations, businesses, the U.S. Census, and the Department of Commerce — indirectly indicating how much will be disposed of in landfills.
The Yale researchers use a more direct method based on numbers reported by the operators of more than 1,200 municipal solid waste landfills, as required by the U.S. Greenhouse Gas Reporting Rule. Landfills didn’t have to report their operational data until 2010; the study used four years of available data, through 2013.
Previous studies have suggested that the EPA underestimated waste disposal in the United States, but the new Yale study’s findings represent the most accurate estimate to date, the researchers said, due to the landfill facility-level data sets used. Powell said the vast majority of landfills have certified scales for weighing garbage, and his data source factored in multiple levels of quality assurance, allowing for a degree of accuracy that was previously unachievable.
“I feel that it’s a superior number to previous estimates, and the key is that we can use our method every year going forward to more accurately track our progress towards more sustainable materials management,” Powell said.
The authors determined that the average landfill has about 33 years of capacity remaining, but their data showed that nationwide disposal capacity is growing.
“I think the disposal rate and capacity numbers are interesting on their own, but I think in the bigger picture, it provides us a distinct, data-driven roadmap for where we can target emissions reductions in the waste sector,” Powell said.
The study used the same data to examine how effective landfills are at capturing landfill gas. Both the United States and many European nations require active landfills to capture the gas they emit, but have had limited means of measuring their success. The researchers found that closed landfills were 17% more efficient at capturing gas than operating landfills. That’s significant because the authors also found that 91% of all landfill methane emissions come from open sites.
The decomposition of municipal waste in landfills is considered one of the largest sources of human-produced methane emissions in the world, accounting for approximately 18% of domestic emissions. The capture and combustion of landfill methane at these facilities is critical to reducing greenhouse gasses produced by landfills, especially since the new estimate strongly suggests that we will continue to rely heavily on landfills for municipal waste management. The authors note that improving the capture of methane gas is particularly important in lower- and lower-middle-income developing nations, where waste generation is expected to increase 185% and 158%, respectively, by 2025.