Wastewater treatment plants in the U.S. clean trillions of gallons of water each year. Whatever water gets drained down sinks or flushed down toilets goes through these plants to be rendered clean enough to return to the environment.
A study by researchers from Northwestern University and the University of Illinois Urbana-Champaign analyzed data from more than 15,000 wastewater treatment facilities – the great majority of all such facilities in the country – to understand the climate costs associated with all this cleaning.
The study estimates that American wastewater treatment plants emit the equivalent of over 50 million tons of carbon dioxide each year. This is expressed as CO2 equivalents because in fact the majority of emissions are in the form of methane and nitrous oxide, which are both powerful greenhouse gases.
Wastewater treatment plants commonly break down solids – like sewage sludge – via anaerobic digestion. Anaerobic digestors often leak, emitting methane. Treatment plants often use a process called nitrification-denitrification in order to limit the amount of excess nitrogen getting into bodies of water. That process releases nitrous oxide.
The study suggested ways to reduce the emissions from wastewater treatment plants including such actions as identifying and repairing leaks in anaerobic digesters and harvesting nitrogen directly from wastewater for use in products such as fertilizer.
With the world population continuing to grow and public sanitary services expanding, reducing the emissions from wastewater treatment plants is an increasingly important necessity for reaching climate targets.
