Engineers from the University of Michigan and Rice University believe water desalination plants (plants that remove salt from water) could replace harsh chemicals with new carbon cloth electrodes. The technology is a new way to remove boron from seawater, an important step in turning saltwater into safe, drinkable water.

Drinkable Water Device

“Most reverse osmosis membranes don’t remove very much boron, so desalination plants typically have to do some post-treatment to get rid of the boron, which can be expensive,” said Jovan Kamcev, U-M assistant professor and a co-corresponding author of the study. “We developed a new technology that’s fairly scalable and can remove boron in an energy-efficient way compared to some of the conventional technologies.”

Boron, a natural element in seawater, can become a harmful contaminant in drinking water when it bypasses standard salt-removal filters. Seawater contains boron levels roughly double the World Health Organization’s maximum safe limit for drinking water. This is five to twelve times higher than what many agricultural plants can tolerate.

Jovan Kamcev inserts a carbon cloth electrode into a flow cell for water desalination; Photo: Marcin Szczepanski, Michigan Engineering.

In ocean water, boron exists as neutral boric acid. It passes through reverse osmosis membranes that typically remove salt by repelling ions. To avoid this, desalination plants normally add a base to treated water, which causes the acid to become negatively charged. Another reverse osmosis stage removes the newly charged boron, and the base is neutralized by adding acid. However, researchers say these extra steps are costly.

Weiyi Pan is a postdoctoral researcher at Rice University and and co-first author of the study. She said, “Our device reduces the chemical and energy demands of seawater desalination, significantly enhancing environmental sustainability and cutting costs by up to 15 percent, or around 20 cents per cubic meter of treated water.”

According to the researchers, the new membranes could save around $6.9 billion annually. Larger desalination plants could potentially save millions of dollars in a year.

The Science Behind it All

To capture boron, a negative charge is first needed. Instead of adding chemicals, this is done by splitting water between two electrodes. This process creates positive hydrogen ions and negative hydroxide ions. The hydroxide ions attach to the boron, giving it a negative charge that makes it stick to capture sites inside the positive electrode’s pores.

Using this method allows treatment plants to avoid using extra energy for another round of reverse osmosis. Afterward, the hydrogen and hydroxide ions combine again to form neutral, boron-free water.

“Our study presents a versatile platform that leverages pH changes that could transform other contaminants, such as arsenic, into easily removable forms,” said Menachem Elimelech, the Nancy and Clint Carlson Professor at Rice University and a co-corresponding author of the study.

“Additionally, the functional groups on the electrode can be adjusted to specifically bind with different contaminants, facilitating energy-efficient water treatment,” Elimelech said.