New Technology Enables Less Hazardous Waste in Desalination

A study published in Nature Chemical Engineering explores how desalination facilities, a critical source of freshwater in arid regions, could reduce hazardous waste by using electricity and new membranes developed at the University of Michigan.

The membranes could help desalination plants reduce or eliminate the brine waste produced as a byproduct of converting seawater to drinking water. Currently, brine waste is stored in ponds for evaporation, leaving solid salt or concentrated brine that can be further processed, though evaporation can be slow and may lead to groundwater contamination.

Space constraints are also a concern, as every liter of drinking water produced at a typical desalination plant generates 1.5 liters of brine. According to a UN study, over 37 billion gallons of brine waste are produced globally each day. When there is insufficient space for evaporation ponds, desalination facilities often inject brine underground or discharge it into the ocean, potentially increasing salinity and impacting marine ecosystems.

There is a big push in the desalination industry for a better solution. Our technology could help desalination plants be more sustainable by reducing waste while using less energy.

Jovan Kamcev, Study Corresponding Author and Assistant Professor, University of Michigan

To minimize brine waste, desalination engineers aim to concentrate the salt so it can crystallize in industrial vats instead of large evaporation ponds. The separated water could be used for drinking or agriculture, while the solid salt can be collected for other uses. In addition to sodium chloride (table salt), seawater contains valuable metals like lithium for batteries, magnesium for alloys, and potassium for fertilizers.

Current methods, such as reverse osmosis and boiling, require significant energy and are limited to relatively low salinity. Electrodialysis, which operates at higher salt concentrations and uses less energy, presents a potential alternative. This process uses electricity to concentrate salt, with water passing through multiple channels separated by membranes. Each membrane has the opposite electrical charge as its neighboring membranes. Positive ions are drawn toward the negative electrode, while negative ions move toward the positive electrode, resulting in streams of purified water and concentrated brine.

However, electrodialysis faces challenges with high salinity, as ions can leak through membranes at elevated concentrations. While some leak-resistant membranes are available, they tend to transfer ions slowly, making energy requirements unsustainable for brines with concentrations more than six times that of seawater.

The researchers addressed this challenge by packing a higher density of charged molecules into the membrane, enhancing its ion-repelling capacity and conductivity. This modification allows the membranes to transfer more salt with less electricity, making them ten times more conductive than current commercial membranes.

The researchers also developed a way to control the membranes' swelling, which typically occurs when water molecules dilute the charge. By incorporating carbon linkages, the membranes remain stable and prevent excessive swelling. The level of restriction can be adjusted, balancing membrane leakage and conductivity. The researchers believe the customizability of these membranes will improve their practical application.

Each membrane isn’t fit for every purpose, but our study demonstrates a broad range of choices. Water is such an important resource, so it would be amazing to help to make desalination a sustainable solution to our global water crisis.

David Kitto, Study First Author and Postdoctoral Fellow, University of Michigan

The study was financed by the US Department of Energy and used NSF-funded X-ray facilities at the University of Pennsylvania Materials Research Science and Engineering Center.

The team applied for patent protection with the help of U-M Innovation Partnerships.

Vdeo Credit: Michigan Engineering

Journal Reference:

Kitto, D. et al. (2025) Fast and selective ion transport in ultrahigh-charge-density membranes. Nature Chemical Engineering. doi.org/10.1038/s44286-025-00205-x