Wastewater Sector Emits Nearly Twice As Much Methane As Previously ThoughtMunicipal wastewater treatment plants emit nearly double the amount of...Wastewater Sector Emits Nearly Twice As Much Methane As Previously Thought
Municipal wastewater treatment plants emit nearly double the amount of methane into the atmosphere than scientists previously believed, according to new research from Princeton University. And since methane warms the planet over 80 times more powerfully than carbon dioxide over 20 years, that could be a big problem.
“The waste sector is one of the largest anthropogenic sources of methane in the world,” said Mark Zondlo, professor of civil and environmental engineering and associated faculty at the Andlinger Center for Energy and the Environment. “As cities continue to urbanize and develop net-zero plans, they can’t ignore the liquid wastewater treatment sector.”
Zondlo led one of two new studies on the subject, both reported in papers published in Environmental Science & Technology. One study performed on-the-ground methane emissions measurements at 63 wastewater treatment plants in the United States; the other used machine learning methods to analyze published literature data from methane monitoring studies of various wastewater collection and treatment processes around the globe.
“Not many people have studied the methane emissions associated with wastewater infrastructure, even though we know that it’s a hotspot for methane production,” said Z. Jason Ren, who led the second study. Ren is a professor of civil and environmental engineering and the Andlinger Center for Energy and the Environment.
The Intergovernmental Panel on Climate Change (IPCC) has established guidelines that allow researchers and institutions like the U.S. Environmental Protection Agency (EPA) to estimate methane emissions from wastewater treatment plants based on their specific treatment processes. However, those guidelines were developed from limited measurements at a relatively small number of wastewater treatment plants.
And when the researchers used the Princeton Atmospheric Chemistry Experiment (PACE) Mobile Laboratory to quantify plant-wide emissions by measuring the plumes of 63 treatment plants on the east coast and in California, they found that the IPCC guidelines consistently underestimated treatment plants of all sizes and treatment processes.
If the results from those 63 plants are representative, actual methane emissions from wastewater treatment facilities across the U.S. would be about 1.9 times greater than emissions estimates that use existing IPCC and EPA guidelines, meaning that those guidelines underestimate methane emissions equivalent to 5.3 million metric tons of carbon dioxide.
Interestingly, the research team who performed the second independent study to analyze literature data on methane emissions came to a similar conclusion: estimated methane emissions from municipal wastewater treatment in the U.S. were around double of what existing guidelines would predict.
“We were able to show, using two different approaches, that methane emissions are a much bigger issue for the wastewater sector than previously thought,” Ren said.