Princeton University researchers report that many countries are undercounting emissions of gases from wastewater treatment plants, including methane and nitrous oxide, by amounts ranging from 19% to 27%. The study, published in Nature Climate Change, finds that outdated inventory methods and omitted emission sources are key reasons for the discrepancy.
The research team examined reporting from 38 countries across five continents. Twenty-six of the countries were economically developed, while 12 were emerging economies. They found that emissions of methane and nitrous oxide from wastewater systems are likely higher than what national climate inventories show. The gap emerged because many inventories still rely on guidance from 2006, even though more recent methods released after 2019 reflect improved scientific understanding of how wastewater systems release gases.
Z. Jason Ren, who led the research and is a professor of civil and environmental engineering and the Andlinger Center for Energy and the Environment at Princeton, said accurate emission data are crucial for policy and technology decisions. “If you don’t know exactly how much emissions you have, then it’s really difficult to make effective policies or technologies or methods to reduce the emissions,” he said.
The team used updated evaluation techniques to assess emissions from large facilities such as sewage treatment plants and from untreated sewage discharge points. After identifying shortfalls in current inventories, researchers estimated that about 94 to 150 million metric tons of carbon dioxide equivalent are missing from annual global emissions data due to gaps in accounting.
Ren noted that wastewater systems are among the largest emitters of methane and nitrous oxide and also require substantial energy and materials to operate. He said that because treatment infrastructure can remain in use for decades, choices made today about technology and emissions management will have prolonged effects. “If you don’t have an accurate accounting, it’s hard to make good and right decisions, yet such decisions can have long-lasting impacts,” he added.
Researchers highlighted that wastewater systems offer opportunities to reduce emissions because they have not been studied as fully as sectors like transportation or power generation. Updating reporting methods to align with current scientific understanding may help countries better track their greenhouse gas outputs and support more targeted reduction strategies.
