Researchers at Princeton Engineering have discovered that wastewater can replace clean water as a feedstock for hydrogen production, potentially cutting water treatment costs by up to 47% and addressing a key limitation in the hydrogen economy. The findings, published in the journal Water Research on September 24, demonstrate a promising pathway for decarbonising hard-to-electrify sectors such as steel and fertiliser manufacturing.

Led by Z. Jason Ren, professor of civil and environmental engineering and the Andlinger Center for Energy and the Environment, the study explores whether treated wastewater could substitute the clean water typically required for electrolytic hydrogen production. “Hydrogen infrastructure generally competes with local fresh water use,” Ren explained. “But every town has a wastewater treatment plant, and that’s a very distributed source of water for the hydrogen economy.”

Green hydrogen, produced through water electrolysis powered by renewable energy, splits water into hydrogen and oxygen gases. The process requires ultrapure water, which adds cost and places additional pressure on freshwater supplies. Currently, most hydrogen produced in the United States is “blue hydrogen,” generated using natural gas with partial carbon capture. While this offers a lower-carbon alternative to direct fossil fuel use, green hydrogen remains the cleaner, long-term solution.

To make the process more sustainable, Ren’s team tested whether “reclaimed” wastewater—treated to a quality suitable for industrial reuse—could directly replace purified water in a proton exchange membrane (PEM) electrolyser. Earlier attempts to use reclaimed water failed due to performance degradation, but the Princeton team set out to identify why. Doctoral researcher Lin Du conducted a series of diagnostic experiments combining electrochemical testing and microscopic imaging to compare electrolyser performance using pure and reclaimed water.

The researchers found that while reclaimed water initially performed well, system efficiency dropped quickly. Detailed analyses revealed calcium and magnesium ions—the same minerals that cause scale buildup in household faucets—as the main culprits. These ions accumulated on the electrolyser membrane, obstructing ion transport and reducing performance. By pinpointing this mechanism, the team has opened the door to new approaches for mitigating scaling and improving wastewater-based hydrogen systems.

Source: 

https://engineering.princeton.edu/news/2025/10/28/dirty-water-boosts-prospects-clean-hydrogen