Research has found that wastewater has the potential to serve as an alternative source for hydrogen. This would address a significant limitation of hydrogen fuel and decrease the water treatment expenses associated with hydrogen production by as much as 47 %. The study was published in the journal Water Research.
Reclaimed wastewater is treated to the point where it could be discharged to aquifers or used for irrigation or industrial cooling. Image Credit: Princeton Engineering
The study represents the progress in establishing hydrogen as a viable means to decarbonize sectors that are challenging to electrify, including steel and fertilizer manufacturing.
Z. Jason Ren, the study's lead author, stated that the existing methods for electrolytic hydrogen production require a significant quantity of clean water, which raises expenses and puts pressure on local water resources.
The research team aimed to investigate whether treated water from wastewater treatment facilities could serve as a viable alternative.
Hydrogen infrastructure generally competes with local fresh water use. But every town has a wastewater treatment plant, and that’s a very distributed source of water for the hydrogen economy.
Z. Jason Ren, Study Lead Author and Professor, Civil and Environmental Engineering, Andlinger Center for Energy and the Environment, Princeton University
Generating hydrogen using renewable energy, referred to as green hydrogen, depends on electrolysis to separate water into hydrogen and oxygen gas. Water is introduced into an electrolyzer, where an electric current prompts positively charged hydrogen ions (protons) to migrate from an anode through a specialized membrane to a cathode, where the protons merge with electrons to create hydrogen gas.
The majority of hydrogen produced in the United States today is referred to as blue hydrogen. In this process, natural gas is the energy source, and a portion of the carbon dioxide generated is captured and stored underground. This makes blue hydrogen a more environmentally friendly energy option than direct natural gas use.
Green hydrogen electrolysis utilizes renewable electricity and results in significantly reduced carbon emissions. However, it generally requires ultrapure water, which is obtained by treating tap water or groundwater through reverse osmosis to eliminate impurities that may disrupt the electrolysis process.
The Princeton team investigated the possibility of circumventing the purification process by utilizing treated wastewater instead of tap water. In this context, the wastewater is referred to as "reclaimed," indicating that it has been treated sufficiently to be safely discharged into aquifers or employed for irrigation or industrial cooling.
According to Ren, the approach had previously been attempted but generally did not succeed beyond a short duration. To determine the cause of the failure, Lin Du, a doctoral candidate in Ren's laboratory, conducted meticulously planned diagnostic experiments using a proton exchange membrane water electrolyzer - the identical technology that is presently utilized commercially with ultrapure water.
Du and collaborators employed a blend of electrochemical assessments and sophisticated microscopic imaging techniques to evaluate the efficacy of pure water against reclaimed wastewater within the reactors. They noted a swift decline in system performance when using reclaimed water, whereas the identical configuration with pure water maintained stable operation.
The team pinpointed calcium and magnesium ions - the same minerals responsible for scale accumulation on domestic faucets and kettles - as the primary contributors to performance degradation by experimental and modeling investigations. These ions adhere to the membrane, obstructing ion transport and transforming it from a permeable pathway into a solid barrier.
The researchers proposed a straightforward solution: acidifying the water using sulfuric acid. The resultant acidic buffer is an abundant source of protons that outcompete other ions, thereby preserving ion conductivity, sustaining electrical current, and facilitating continuous hydrogen production.
It’s expensive to remove all those ions, so you have ultrapure water going into the electrolyzer. Now, you can just acidify it a bit, then put ion-containing water into the electrolyzer, and it lasts for more than 300 hours without apparent issues.
Z. Jason Ren, Study Lead Author and Professor, Civil and Environmental Engineering, Andlinger Center for Energy and the Environment, Princeton University
The team projected that utilizing reclaimed wastewater instead of purified water could lower the expenses associated with water treatment for hydrogen production by approximately 47 %, while also reducing the energy costs of that treatment by around 62 %.
“This acid is recirculated, so it’s never getting out of the system, which is important from both an environmental and cost perspective,” said Ren.
Similarly, the calcium and magnesium ions remain soluble without disrupting the circulation.
Ren and team are collaborating with industry partners to evaluate the effectiveness of their approach on a larger scale, as well as its potential application with pretreated seawater as a feedstock.
Last year, the team published a study focused on maximizing both water and cost efficiency in hydrogen production. The study pinpointed the optimal locations in the United States to co-locate hydrogen facilities with wastewater treatment plants where reclaimed water is plentiful. Jinyue Jerry Jiang, a Maeder Graduate Fellow at the Andlinger Center who completed his Ph.D. at Princeton earlier this year, spearheaded this research.
We wanted to really look into the possibility of using reclaimed water to enable a national hydrogen strategy. We do both deep technical research and big-picture analytical work to serve both scientific needs and industry needs.
Z. Jason Ren, Study Lead Author and Professor, Civil and Environmental Engineering, Andlinger Center for Energy and the Environment, Princeton University
Journal Reference:
Du, L., et al. (2025) Electrolytic hydrogen production from acidified wastewater effluent. Water Research. doi.org/10.1016/j.watres.2025.124672