A study detailing the technology has been published in Nature Water by engineers from both institutions.
Boron, a natural component of seawater, poses a challenge for desalination systems. While conventional filters effectively remove salts, they struggle with boron, which is found in seawater at levels twice as high as the World Health Organization's safe drinking water limits and significantly higher than levels tolerated by many crops.
"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," explained Jovan Kamcev, assistant professor of chemical engineering and macromolecular science and engineering at the University of Michigan and 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."
In typical desalination processes, boron exists as neutral boric acid, which passes through reverse osmosis membranes designed to repel charged particles. To remove boron, desalination plants currently add a base to the water, converting boric acid into negatively charged ions. This is followed by another stage of reverse osmosis, after which acid is added to neutralize the water-a costly series of steps.
"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," said Weiyi Pan, a postdoctoral researcher at Rice University and co-first author of the study.
Given the global desalination capacity of 95 million cubic meters per day as of 2019, this innovation could save an estimated $6.9 billion annually. Large facilities like San Diego's Claude "Bud" Lewis Carlsbad Desalination Plant could see millions in yearly savings.
These cost reductions could make seawater a more accessible drinking water source, addressing the global water crisis. According to a 2023 report by the Global Commission on the Economics of Water, freshwater supplies are expected to meet just 40% of demand by 2030.
The new electrodes work by trapping boron within pores equipped with oxygen-containing structures, which selectively bind with boron while allowing other ions to pass through. The boron is given a negative charge by splitting water into positive hydrogen ions and negative hydroxide ions. The hydroxide binds to boron, enabling the electrodes to capture it efficiently. Afterward, the hydrogen and hydroxide recombine to produce neutral, boron-free water. This eliminates the need for an additional reverse osmosis stage, saving energy.
"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, Nancy and Clint Carlson Professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering at Rice University and a co-corresponding author. "Additionally, the functional groups on the electrode can be adjusted to specifically bind with different contaminants, facilitating energy-efficient water treatment."
Research Report:A highly selective and energy-efficient approach to boron removal overcomes the Achilles heel of seawater desalination
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