Water desalination facilities have the potential to substitute costly chemicals with innovative carbon cloth electrodes that effectively eliminate boron from seawater, making it a crucial advancement in converting seawater into safe drinking water.
Engineers from the University of Michigan and Rice University have detailed this groundbreaking technology in a study published in Nature Water.
Boron, a naturally occurring element in seawater, becomes harmful to drinking water when it escapes through standard filters used for salt removal. The concentration of boron in seawater is approximately twice that of the World Health Organization’s most relaxed thresholds for potable water and five to twelve times higher than what many crops can tolerate.
“Many reverse osmosis membranes are not very effective at eliminating boron, requiring desalination plants to perform additional costly treatments,” explained Jovan Kamcev, an assistant professor of chemical engineering and macromolecular science and engineering at U-M and a lead author of the study. “Our innovative technology is fairly scalable and is more energy-efficient in removing boron compared to traditional methods.”
In seawater, boron is present as boric acid, which is electrically neutral, allowing it to bypass reverse osmosis membranes that target charged particles known as ions. To address this challenge, desalination facilities usually add a base to the water, which alters boric acid into a negatively charged form. A subsequent reverse osmosis process then extracts the charged boron, requiring the addition of acid later to neutralize the base. These extra steps can be expensive.
“Our device lowers the chemical and energy requirements for seawater desalination, significantly boosting environmental sustainability and cutting costs by up to 15%, or about 20 cents for every cubic meter of treated water,” said Weiyi Pan, a postdoctoral researcher at Rice University and a co-first author of the study.
With global desalination capacity reaching 95 million cubic meters per day as of 2019, the new membranes could result in savings of approximately $6.9 billion each year. Major desalination plants, like San Diego’s Claude “Bud” Lewis Carlsbad Desalination Plant, could save millions annually.
Such savings might make seawater a more viable resource for drinking water and ease the escalating water shortage crisis. A report from the Global Commission on the Economics of Water indicates that freshwater supplies will only be able to satisfy 40% of demand by 2030.
The novel electrodes trap boron by utilizing pores lined with oxygen-containing groups that specifically bond with boron, while allowing other seawater ions to pass through, thereby maximizing boron capture.
However, these structures still require the boron to carry a negative charge. Instead of introducing a base, this charge is generated by splitting water between two electrodes, which produces positive hydrogen ions and negatively charged hydroxide ions. The hydroxide attaches to boron, imparting it with a negative charge that allows it to adhere to the capture sites within the pores on the positive electrode. This method of capturing boron with the electrodes also permits treatment plants to conserve energy by skipping an additional stage of reverse osmosis. Afterward, the hydrogen and hydroxide ions combine to form neutral, boron-free water.
“Our findings offer a flexible platform that utilizes pH adjustments to convert other contaminants, like arsenic, into forms that can be easily removed,” remarked Menachem Elimelech, the Nancy and Clint Carlson Professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering at Rice University and a co-corresponding author of the research.
“Furthermore, the functional groups on the electrode can be modified to specifically target various contaminants, enhancing the energy efficiency of water treatment,” added Elimelech.
The study received support 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 electrodes underwent analysis at the Michigan Center for Materials Characterization.
