How Much Greenhouse Gas Does Wastewater Treatment Emit? A US Benchmark for Targeted Reduction

Wastewater's Hidden Emissions

Wastewater treatment is essential for protecting public health and water quality, but it also carries a climate footprint. As cities and utilities strive toward net-zero goals, one critical question arises: how much greenhouse gas (GHG) does wastewater treatment emit?

Until now, the answer has been surprisingly hard to pin down. While energy use in treatment plants is tracked relatively well, direct emissions of methane and nitrous oxide—both much more potent than carbon dioxide—have often been overlooked or estimated with limited data. This gap has made it difficult for utilities, regulators, and researchers to know where to focus their efforts in cutting emissions.

Benchmarking Emissions Across US Wastewater Treatment

Our recent study, Benchmarking greenhouse gas emissions from US wastewater treatment for targeted reduction, recently published in Nature Water, provides the first systematic benchmark of GHG emissions from wastewater treatment across the United States. By compiling nationwide data on treatment processes, energy demand, and by-product generation, we quantified the sector’s climate footprint with a level of detail that can guide targeted reductions.

Key findings include:

• Total emissions are substantial. US wastewater treatment facilities emit an estimated ~47 million metric tons of CO₂-equivalents per year, comparable to the annual emissions of about 10 million passenger vehicles.

• Direct process emissions dominate. Roughly 70% of the sector’s footprint comes from methane and nitrous oxide released during biological treatment, with the remainder largely linked to energy use.

• Emissions vary widely by process. Aerobic processes, while effective for pollutant removal, are associated with high nitrous oxide emissions, while anaerobic digestion produces methane that can either be captured for renewable energy or lost to the atmosphere.

• Regional differences matter. Differences in plant size and treatment processes result in a wide variation. Emissions cluster near major cities, with 10% of plants responsible for over 80% of the total emissions.

Here is the contribution of each source to US wastewater treatment emissions (median values, million metric tons CO₂-equivalents per year):

Why This Matters

Benchmarking provides more than just numbers—it creates a roadmap for climate action. Utilities can now compare their emissions against national averages, pinpoint areas of concern, and prioritize upgrades. Regulators and policymakers can use this information to set realistic reduction targets and support investments in low-carbon treatment technologies.

For example, if utilities captured just 50% of fugitive methane losses from anaerobic digesters nationwide, the sector’s total emissions could fall by nearly 15%. Similarly, optimizing aeration strategies to control nitrous oxide formation could cut emissions without major infrastructure changes.

Looking Ahead

Wastewater treatment may not be the first sector people think of when they hear “climate change”, but its role is critical. By shining a light on its GHG emissions, we can integrate wastewater management into broader decarbonization strategies.

The takeaway is clear: we now have a US benchmark for GHG emissions from wastewater treatment. With this foundation, targeted reductions are not just possible—they’re within reach.

Read the Nature Water publication at: https://www.nature.com/articles/s44221-025-00485-w 

Download the full dataset at: https://doi.org/10.5281/zenodo.16745956

Code available at: https://github.com/jiananf2/US_WWTP_GHG