A new application of electrodialysis for desalination may use 90% less energy than its counterparts, according to a press release by the Beckman Institute for Advanced Science and Technology
The new method was developed by researchers at the Beckman Institute. The researchers’ study explored using polymers with reduction-oxidation (redox) properties to replace ion-exchange membranes with nanofiltration membranes, leading to “cheaper and more robust nanofiltration membranes.” The study appears in ACS Energy Letters.
“We need a way to purify drinking water that’s low-energy, inexpensive, and useful for the communities that need it the most. I see our solution as a platform to tackle both the energy and water crises,” said Xiao Su, a Beckman researcher and an assistant professor of chemical and biomolecular engineering at the University of Illinois Urbana-Champaign.
Electrodialysis is an effective desalination tool, but often comes at a high energy cost. This is largely due to its flagship water-splitting reaction, which pulls water molecules apart into two components: a positively charged proton and a negatively charged hydroxide. Because the building blocks of salt have charges of their own, splitting the water forces the mineral’s movement in a designated direction.
Electrodialysis also uses charged ion-exchange membranes, so named because only ions (atoms with a positive or negative electric charge) can pass through. Ion-exchange membranes are one of the costliest components of electrodialysis, as they require diligent upkeep and frequent replacement.
Su and his colleagues sought to purify water without the energy toll of electrodialysis or the financial strain of ion-exchange membranes. So, they modified the traditional approach in two major ways.
To save energy, the researchers streamlined the salt separation process with a chemical phenomenon called a redox reaction. Physically, triggering a redox reaction looks like adding a special polymer-based material to the wastewater before it’s filtered and purified.
Chemically, the results are transformative. Instead of splitting water molecules into positively and negatively charged slices to coax out the salt, the redox reaction changes the charge of the entire water molecule in one fell swoop, achieving the same degree of salty separation with about 90% less energy than traditional water-splitting.
To add economic savings to energy efficiency, the researchers swapped conventional ion-exchange membranes for nanofiltration membrane, a more robust and less expensive option.
Experiments at a regional water treatment plant demonstrated that the researchers’ method can successfully purify wastewater; future plans include expanding into saltwater and brackish water sources like groundwater and rivers.
Due to its low energy requirement, redox-inspired electrodialysis is designed to pair well with solar panels. Its positive performance in hot climates is useful for applications in climate-affected regions, “where low-cost, low-energy desalination is very much needed,” Su said.
“Water scarcity is a global problem, and it’s not going to change in a day. But we are taking a step toward a solution that is feasible and capable of being scaled up,” he said.
So far, the researchers have tested their method on samples of multiple liters. But they are eager to expand into a bigger pond.
“We have the right polymer, we have the right membrane, and we have the right conditions,” Su said. “The science is there, so the next step is paving a way for deploying these devices for real-world water treatment. I believe the time is right for that, and I’m excited to see it happen.”
