A breakthrough in water desalination could reduce the need for costly chemicals by employing advanced carbon cloth electrodes to eliminate boron from seawater, a crucial step in transforming seawater into potable water.
The findings, which highlight this new method, have been published in Nature Water and are the result of collaboration between engineers from the University of Michigan and Rice University.
Boron is a naturally occurring substance in seawater but becomes harmful when it passes through conventional desalination processes. In seawater, boron levels are typically twice as high as the World Health Organization’s acceptable limits for drinking water, and five to twelve times higher than what many crops can tolerate.
“Most reverse osmosis membranes are not very effective at removing boron, so desalination plants generally need to use additional treatment steps to address this issue, which can drive up costs,” explained Jovan Kamcev, assistant professor of chemical engineering and macromolecular science and engineering at the University of Michigan and a co-corresponding author of the paper. “Our new technology is scalable and offers a more energy-efficient way to remove boron compared to traditional methods.”
Boron exists in seawater as boric acid, which is electrically neutral, allowing it to pass through reverse osmosis membranes designed to reject electrically charged particles (ions). To tackle this challenge, desalination plants usually add a base to the treated water, which converts boric acid into a negatively charged form. This then undergoes another reverse osmosis stage, followed by neutralization with acid. These additional steps increase the cost of desalination.
“Our system lowers the chemical and energy requirements for seawater desalination, offering substantial environmental benefits while reducing costs by up to 15 percent, or roughly 20 cents per cubic meter of water processed,” said Weiyi Pan, a postdoctoral researcher at Rice University and one of the lead authors of the study.
With global desalination capacity reaching 95 million cubic meters per day in 2019, this new technology could save approximately $6.9 billion each year. Large facilities, like the Claude “Bud” Lewis Carlsbad Desalination Plant in San Diego, could potentially save millions annually.
Such savings could make seawater desalination a more viable option for providing drinking water and help address the escalating global water scarcity. A 2023 report from the Global Commission on the Economics of Water predicts that freshwater will only meet 40% of global water demand by 2030.
The novel electrodes work by trapping boron within specialized pores containing oxygen-based structures, which specifically attract boron while allowing other ions to pass. This process enhances the electrode’s capacity to capture boron.
The electrodes, however, still require boron to be negatively charged. Rather than adding a base, this charge is generated by splitting water at two electrodes, creating positive hydrogen ions and negative hydroxide ions. The hydroxide ions then bind to boron, making it negatively charged, allowing it to be captured by the positive electrode’s pores. This process eliminates the need for an additional reverse osmosis step, reducing energy consumption. The result is clean, boron-free water.
“This research introduces a flexible platform that utilizes pH changes, which could potentially be adapted to remove other contaminants, such as arsenic, in a similarly efficient manner,” said Menachem Elimelech, Nancy and Clint Carlson Professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering at Rice University, and co-corresponding author.
“The electrode’s functional groups can be modified to target a range of contaminants, enhancing the overall energy efficiency of water treatment,” he added.
The study received funding from the National Alliance for Water Innovation, the U.S. Department of Energy, the U.S. National Science Foundation, and the U.S.-Israel Binational Science Foundation. The research on the electrodes was conducted at the Michigan Center for Materials Characterization.
