(This article was produced in partnership with the Energy News Network, a nonprofit news site that covers the transition to a clean energy economy from state and regional perspectives.)
How much does household waste fuel the climate crisis? Official numbers suggest a small role, but the full contribution is not yet known — even by regulators and scientists.
As New England states work to curb greenhouse gas emissions from transportation and heating, little attention goes to landfills and municipal solid waste, or “waste-to-energy,” incinerators. Combined, those sources typically represent 5 percent or fewer of each state’s total emissions, and they get scarce mention in climate action plans.
But growing volumes of plastics in the waste stream complicate incinerator emissions accounting. Fewer than 9 percent of plastics are recycled, and global plastic production is expected to double by 2040.
Plastic combustion produces many more byproducts than the three greenhouse gases that most incinerators report annually to the U.S. Environmental Protection Agency (EPA): carbon dioxide (CO2), nitrous oxide and methane.
Some chemical compounds in plastics don’t appear to degrade during incineration, while others break down partially and recombine, potentially forming potent and enduring greenhouse gases — compounds that are thousands of times more effective at trapping heat than CO2 and can linger in the atmosphere for millenia.
Scientists do not yet know the scale of the problem, but a growing body of research suggests that even small amounts of these powerful warming agents could have a significant impact.
The Northeast is the hub of U.S. waste incineration
The Northeast is home to roughly half of the nation’s 75 waste-to-energy incinerators, most of which were constructed in the 1980s and are now passing their expected 30-year lifespans.
These facilities typically operate around the clock, feeding waste into boilers that generate steam to produce electricity and that release pollutants in the form of gaseous emissions, fly ash, bottom ash and leachate.
All three states award municipal waste incinerators renewable energy certificates for their electricity generation, crediting the facilities for helping to avoid the higher methane emissions from landfills. Without factoring in avoided emissions, a recent “cradle-to-gate” life cycle assessment of a waste incinerator outside Syracuse, New York found its climate impact was comparable to “that of electricity from fossil fuels.”
Municipal waste incinerators typically burn a mix of consumer waste, with little control over what dump trucks bring in. “We are a reflection of our residents,” said Matt Grondin, communications manager for the ecoMaine incinerator in Portland, Maine; whatever is in household trash at a third of the state’s homes ends up at its facility. That ever-changing, heterogenous mix of waste makes it hard to gauge what incinerators emit.
More estimating than monitoring
Waste that derives from fossil fuels — like plastics and synthetic fibers — contributes most of the carbon emissions from incineration. That portion is commonly a third to a half of what gets burned, an Intergovernmental Panel on Climate Change (IPCC) paper noted. Given the shifting mix of waste, the IPCC added, “continuous monitoring” to track greenhouse gas emissions would be ideal.
The EPA currently mandates that municipal waste incinerators report emissions annually for just three greenhouse gases, using default formulas the agency set in 2009. Based on those formulas, the EPA calculated that the nation’s waste incinerators in 2019 released 20.2 million tons of CO2, the equivalent annual emissions of about 5 coal-fired plants.
States that require reporting of additional greenhouse gases typically rely on estimates as well, rather than direct testing or ongoing monitoring.
‘Forever chemicals’ could have major climate impact
Municipal waste incinerators depend on plastic waste because it burns efficiently, helping keep temperatures hot. But its combustion produces numerous hazardous compounds. Among the most concerning constituents are fluoropolymers, part of the PFAS (per- and polyfluoroalkyl substances) family of compounds dubbed “forever chemicals” due to their persistence in the environment and resistance to heat, water and oil.
The waste stream fueling incinerators now includes countless consumer items containing PFAS — from pizza boxes, takeout food containers and personal care products to clothing, electronics and nonstick cookware. And while waste incinerators are not generally equipped to handle construction debris or hazardous waste, materials like coated wire, carpeting, spray foam insulation, paint and PVC pipe do get incinerated.
Fluoropolymers are notorious for having strong carbon-fluorine bonds. Even at temperatures over 1,800 degrees F, which not all incinerators consistently achieve, the chemicals may not fully break down. Their partial breakdown can lead to the formation of numerous problematic compounds, including fluorinated gases like hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) — which remain in the atmosphere for hundreds to thousands of years, heating it far more effectively than CO2.
The potential for inadvertent release of highly potent atmospheric gases and other byproducts of concern was first highlighted in a 2001 Canadian study, and a 2003 study examining the breakdown of fluoropolymers like PTFE (known by the brand name Teflon) found “a plethora of unidentified and previously unreported materials.” A 2009 Norwegian literature review reinforced these findings.
Researchers in a 2015 study that simulated incineration’s impact on Dupont-made “Nafion” membrane, which includes PTFE, detected “several types of PFCs.”
‘We don’t really know what’s actually emitted’
A 2020 EPA technical brief stated that “the effectiveness of incineration to destroy PFAS compounds and the tendency for formation of fluorinated or mixed halogenated organic byproducts is not well understood.” In webinars, agency staff members have acknowledged the need for “comprehensive research” into “emissions rates, composition and activity data from unconstrained sources like industrial facilities using PFAS [and] incinerators.”
EPA’s 2019 PFAS Action Plan and 2021-2024 PFAS Strategic Roadmap contain no references to waste incineration, and “EPA is not doing research directly on PFAS contributing to greenhouse gases,” according to a spokesperson for the agency’s Office of Research and Development.
In-house pilot studies begun by the EPA’s Center for Environmental Measurement and Modeling are researching ways to measure PFAS in air emissions. Initial results of introducing some compounds into a small research combustor showed that carbon tetrafluoride (CF4), a potent greenhouse gas 6,500 times stronger than CO2 with an atmospheric lifetime of 50,000 years, was “particularly difficult to destroy,” researchers reported.
Small-scale combustion experiments don’t reflect conditions in municipal solid waste incinerators, which vary widely in their burn temperatures and means of filtering out emissions through scrubbers and electrostatic precipitators, said Lydia Jahl, Science and Policy Associate at the Green Science Policy Institute. Testing should be done routinely at each facility to assess a broad spectrum of pollutants, she added, given the wide array of harmful substances plastic combustion can release.
“Lack of [testing] methods is certainly a problem,” observed University of Rhode Island professor Rainer Lohmann, lead author of a recent fluoropolymer study and co-director a collaborative research initiative on PFAS.
“It is certain that upon incineration of PFAS, very volatile fluorine-containing gases will be emitted, and some of those could have a high greenhouse gas potential, and others might be toxic,” he noted. But right now, “we don’t really know what’s actually emitted.”