Researchers have developed carbon cloth electrodes that efficiently remove boron from seawater, potentially replacing costly chemicals in desalination.

The electrodes remove boron from desalinated water by splitting molecules into ions. Hydroxide ions bind to boron, which adheres to positive electrodes, ensuring safer drinking water production.

The breakthrough, developed by a team of engineers at the University of Michigan (UM) and Rice University, marks a crucial advancement in making seawater safe for drinking. 

The technology turns seawater into drinking water with fewer chemicals. Image: University of Michigan.

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

Efficient boron removal from seawater 

Boron, a natural seawater component, becomes a toxic contaminant in drinking water when it bypasses conventional salt-removing filters. Seawater’s boron levels often exceed the World Health Organization’s limits for safe drinking water and surpass the tolerance of many agricultural plants.

Conventional reverse osmosis membranes struggle to remove boron, as it exists in seawater as electrically neutral boric acid, which passes through filters designed to repel charged particles.

“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,” said Jovan Kamcev, assistant professor of chemical engineering and macromolecular science and engineering at UM and a co-corresponding author of the study, in a statement. 

The diagram illustrates how the researchers’ electrodes remove boron. Initially, most salt ions are removed through reverse osmosis.

In order to solve this problem, desalination plants usually add a base to change boric acid into a negatively charged form. After removing this charged boron in a second step of reverse osmosis, the base is neutralised using acid. But the expense of these other procedures goes up a lot.

The new device simplifies the process, reducing the need for extra chemicals and energy. This innovation enhances environmental sustainability and lowers costs by up to 15%, saving about 20 cents per cubic metre of treated water. 

Sustainable water solutions

Global desalination capacity reached 95 million cubic meters per day in 2019, and new membranes designed for boron removal could save approximately $6.9bn annually.

The team highlights that large-scale facilities, such as San Diego’s Claude 'Bud' Lewis Carlsbad Desalination Plant, stand to save millions of dollars per year.

These cost reductions could make seawater a more viable source of drinking water, addressing the escalating global water crisis. Freshwater supplies are projected to meet just 40% of demand by 2030, according to a 2023 report by the Global Commission on the Economics of Water.

The advanced electrodes efficiently remove boron by trapping it within pores lined with oxygen-containing structures that specifically bind to boron while allowing other ions to pass through. However, boron must carry a negative charge to adhere to the capture sites. 

The electrodes create positive hydrogen ions and negative hydroxide ions by splitting water between two layers rather than by introducing a chemical base to induce this charge. By binding with boron, the hydroxide provides the charge required for it to adhere to the positive electrode. By doing away with the requirement for a second reverse osmosis step, this method lowers expenses and energy consumption.

After the boron is eliminated, hydrogen and hydroxide ions recombine to create neutral, boron-free water, offering a sustainable and effective method of desalinating saltwater.

“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, a professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering at Rice University, and a co-corresponding author of the study, in a statement.

Additionally, the functional groups on the electrode can also be modified to specifically bind with various contaminants, enabling more energy-efficient water treatment.

The details regarding the team’s research were published in the journal Nature Water.