The high economic and energy costs incurred by desalination systems are addressed with an optimized electrodialysis process devised by researchers from Kongju National University (South Korea) and the University of Illinois. Process improvements derived from the use of a cellulose-based nanofiltration membrane in place of the traditional ion-exchange membrane, and a water-soluble polymer in wastewater to alter the electrical charge.

The nanofiltration membrane is stable against organic pollutants and does not foul, making it much more robust. The economics of this component are also a plus, as its cost is 10% of that of a traditional ion-exchange membrane. The water-soluble polymer alters the electrical charge and attracts salt without splitting water molecules. Modeled from the redox flow battery process, the polymer solution reduces energy consumption by 88% when compared to traditional electrodialysis.

During testing, increasing the voltage from 0.6 V to 0.8 V resulted in an increase in desalination from 69% to 119%. Raising the room temperature from 5° C to 21° C and 60° C achieved 1.19-times and 1.33-times higher salt removal, respectively. In geographically favorable locations with hot climates, the prototype can naturally operate at higher temperatures and take advantage of increased desalination rates.

When treating an equal volume of 100 m³ of wastewater, the polymer-nanofiltration membrane prototype costs $0.134/m³ compared to $1.02/m³ for traditional electrodialysis, up to $2.6/m³ for distillation, and $1.7/m³ for reverse osmosis.

The modular system described in ACS Energy Letters can be installed in a cascading fashion, where the wastewater flows through one segment then the other, each removing a portion of the salt until the water reaches the desired desalination levels. This keeps voltage low within each stage and still achieves the required desalination rates.