A new innovation in water desalination technology has the potential to reduce costs and improve sustainability by replacing costly chemical treatments with new carbon cloth electrodes.
The development is spearheaded by engineers from the University of Michigan and Rice University, and their work is detailed in a recent study published in Nature Water.
The Challenge of Boron in Seawater
Boron, a naturally occurring element in seawater, poses significant challenges for desalination efforts. When present in drinking water, it becomes a toxic contaminant. Conventional reverse osmosis filters, typically used to remove salts, allow electrically neutral boric acid — the form of boron found in seawater — to pass through. Seawater contains boron levels that often exceed the World Health Organization’s recommended limits for safe drinking water by more than double, and they far surpass the tolerance levels for many agricultural plants, according to the researchers.
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To address this, desalination plants traditionally employ costly post-treatment steps. These involve adding a base to convert boric acid into a negatively charged ion, which can then be removed through another reverse osmosis stage. The base is subsequently neutralized with acid, further increasing costs and energy consumption.
A New Solution: Carbon Cloth Electrodes
The new technology developed by the research team is said to offer a more efficient and cost-effective alternative.
“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, an assistant professor of chemical 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.”
The system uses specially treated carbon cloth electrodes to trap boron ions. Acid treatment endows the fibres with oxygen-containing structures that bind selectively with boron, while allowing other ions to pass through. This targeted approach maximizes boron capture efficiency.
Instead of relying on chemical additives, the process uses water splitting to create hydroxide ions that give boron a negative charge, making it adhere to the positive electrode. The hydroxide ions recombine with hydrogen ions after boron removal, yielding neutral, boron-free water. This eliminates the need for additional reverse osmosis stages, cutting energy use and costs.
Significant Cost and Sustainability Benefits
The researchers estimate that their system could reduce desalination costs by up to 15%, equating to approximately $0.20 per cubic metre of treated water. Given the global desalination capacity of 95 million cubic metres per day as of 2019, this could translate to an annual savings of $6.9 billion, says the research team. Large facilities, such as San Diego’s Claude “Bud” Lewis Carlsbad Desalination Plant, could save millions annually.
“Our device reduces the chemical and energy demands of seawater desalination, significantly enhancing environmental sustainability,” said Weiyi Pan, a postdoctoral researcher at Rice University and co-first author of the study.
Broader Implications for Water Treatment
This research could help address the growing global water crisis. Freshwater supplies are projected to meet only 40% of demand by 2030, according to the Global Commission on the Economics of Water.
Additionally, the platform’s versatility extends beyond boron removal. “Our study presents a versatile platform that leverages pH changes that could transform other contaminants, such as arsenic, into easily removable forms,” noted Menachem Elimelech, a professor of civil and environmental engineering at Rice University and co-corresponding author.
The functional groups on the electrodes can also be tailored to target different contaminants, potentially transforming water treatment technologies, the researchers explained.
In fall 2024, the University of Waterloo’s Department of Chemical Engineering developed a device that mimics the natural water cycle, where water evaporates and condenses, preventing salt accumulation that typically hampers most desalination systems, the researchers said. Made of nickel foam coated with a conductive polymer and thermoresponsive pollen particles, the researchers explain that their portable device can produce 18 to 22 litres of fresh water per square metre per day.
