In a breakthrough that could make clean energy more practical and affordable, researchers at Princeton University have found a way to use treated wastewater—rather than clean drinking water—to produce hydrogen fuel.
The discovery could cut water treatment costs nearly in half and make hydrogen a more sustainable energy source for industries like steel and fertilizer production.
The study, published in Water Research, was led by Professor Z. Jason Ren from Princeton’s Department of Civil and Environmental Engineering and the Andlinger Center for Energy and the Environment.
Ren explained that hydrogen production currently relies on large amounts of purified water, which is costly and competes with local freshwater supplies.
“Every town has a wastewater treatment plant,” he said. “That’s a distributed, renewable water source that could power the hydrogen economy.”
Hydrogen can be made in different ways. Today, most hydrogen in the United States is “blue hydrogen,” produced from natural gas with some carbon emissions captured and stored underground.
A cleaner option is “green hydrogen,” which uses electricity from renewable sources like wind or solar to split water into hydrogen and oxygen through electrolysis. However, electrolysis usually requires ultrapure water, adding extra cost and energy use for purification.
Ren’s team wondered if treated wastewater—already cleaned enough to be reused for irrigation or industrial cooling—could replace pure water in the process.
Earlier attempts to use wastewater had failed because electrolyzers, the machines that split water, quickly lost efficiency. To find out why, Ph.D. student Lin Du and colleagues ran detailed experiments using both pure and reclaimed water in a proton exchange membrane electrolyzer.
They discovered that minerals commonly found in wastewater, such as calcium and magnesium, were clogging the electrolyzer’s membrane—just like how mineral buildup blocks household faucets.
These ions stuck to the surface, preventing the flow of hydrogen ions and shutting down the system.
The researchers came up with a simple but effective fix: adding a small amount of sulfuric acid to the water. This makes the water slightly acidic, creating extra hydrogen ions that outcompete calcium and magnesium.
With this tweak, the system ran smoothly for over 300 hours without performance loss.
The results showed that using reclaimed wastewater could lower water treatment costs for hydrogen production by 47% and energy use by about 62%. Even better, the acid is recycled within the system, so it doesn’t create additional waste.
Ren’s team is now working with industry partners to test the method on a larger scale, including exploring whether pretreated seawater could be used.
“We’re combining deep technical research with big-picture analysis to make hydrogen production both cost-effective and sustainable,” Ren said. “This could be a key step toward a cleaner energy future.”
