Innovative carbon cloth electrodes may revolutionize water desalination by effectively removing boron from seawater, a crucial advancement for producing safe drinking water. A study in Nature Water by University of Michigan and Rice University engineers outlines this breakthrough. Boron, a natural seawater component, poses a challenge as it turns toxic in drinking water, surpassing the World Health Organization’s safety limits and exceeding agricultural plant tolerance levels.
“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, assistant professor of chemical engineering and of macromolecular science and engineering in the College of Engineering and a co-corresponding author of the study.
This new technology offers a scalable method to remove boron efficiently, circumventing the need for costly post-treatment. Boron in seawater exists as neutral boric acid, passing through typical reverse osmosis membranes designed to filter ions. To address this, desalination plants usually add a base, charging the boron for removal, adding expense.
“Our device reduces the chemical and energy demands of seawater desalination, significantly enhancing environmental sustainability and cutting costs by up to 15%, or around 20 cents per cubic meter of treated water,” said Weiyi Pan, a postdoctoral researcher at Rice University and a study co-first author.
With a global desalination capacity of 95 million cubic meters daily in 2019, these membranes could save $6.9 billion annually. Large plants, like San Diego’s Claude “Bud” Lewis Carlsbad Desalination Plant, might save millions annually. This innovation could ease the global water crisis, with freshwater supplies projected to meet just 40% of demand by 2030.
The electrodes trap boron in pores with oxygen structures binding selectively, allowing other ions to pass. Boron needs a negative charge, achieved by splitting water between electrodes, creating hydrogen and hydroxide ions. The negative hydroxide bonds with boron, allowing it to stick to the electrode’s capture sites.
Capturing boron this way eliminates the need for additional reverse osmosis stages, recombining ions to produce 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.
The research, supported by 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, was conducted at the Michigan Center for Materials Characterization.
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