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Desalination plants are increasingly recognized as vital facilities for producing freshwater in arid regions. Recent advancements in technology at the University of Michigan suggest that these plants could significantly reduce or even eliminate harmful brine waste.
Currently, desalination processes generate liquid brine as a byproduct, which is typically stored in evaporation ponds until the water evaporates, leaving behind solid salt or concentrated brine for further processing. However, this method is not without risks; brine can potentially leach into groundwater and contaminate it over time.
Space limitations also present significant challenges. For every liter of potable water produced by conventional desalination methods, approximately 1.5 liters of brine is generated. According to a United Nations report, over 37 billion gallons of brine waste is produced globally each day. In regions without adequate space for evaporation ponds, some facilities resort to underground injection or ocean disposal, which can elevate local salinity levels and disrupt marine ecosystems.
Jovan Kamcev, an assistant professor of chemical engineering at U-M and co-author of a newly published study in Nature Chemical Engineering, emphasized the pressing need for innovative solutions in the desalination sector. “Our technology could enhance sustainability in desalination by cutting down on waste and reducing energy consumption,” he stated.
To tackle brine waste effectively, engineers are exploring ways to concentrate the salt, allowing for crystallization in industrial vats instead of sprawling evaporation ponds. This concentrated output could be utilized for various applications, including drinking water and agriculture, while the solid residual salt could be harvested for beneficial use. Seawater contains more than just sodium chloride; it is also rich in valuable metals like lithium for batteries, magnesium for lightweight materials, and potassium for fertilizers.
Current methods for brine concentration often involve energy-intensive heating and evaporation processes or reverse osmosis, which works effectively only at lower salinity levels. Electrodialysis presents a promising alternative, functioning at higher salt concentrations and requiring less energy overall. This technique uses electricity to move salt ions, charged atoms or molecules, within the water.
The electrodialysis process involves water flowing through numerous channels separated by oppositely charged membranes, with electrodes situated at both ends. The positive ions gravitate towards the negatively charged electrode, halted by a positively charged membrane, while the negative ions are attracted to the positive electrode and stopped by a negatively charged membrane. This results in two distinct channels for purified water and concentrated brine.
However, traditional electrodialysis has limitations concerning salinity. As salt concentrations increase, ions can leak through the membranes, weakening their effectiveness. Although more resilient membranes are available, they often lack the speed needed for efficient ion transport, particularly at salinities exceeding six times that of average seawater.
The researchers at U-M have addressed this challenge by densely packing charged molecules into their new membranes, enhancing both ion-repelling capabilities and conductivity. Their innovative design can achieve membrane conductivity levels up to ten times greater than existing commercial options.
A conventional issue limiting membrane efficiency is swelling, which occurs as water molecules are absorbed, diluting the charge. The new membranes counter this by employing carbon connectors that maintain the integrity of the charged molecules and prevent excessive swelling.
The customizable nature of these membranes allows researchers to adjust levels of leakiness and conductivity, potentially surpassing current commercial membrane performance. David Kitto, a postdoctoral fellow in chemical engineering and the study’s lead author, expressed hope for the future: “While each membrane may have specialized applications, our findings highlight a diverse range of options. Given the pressing need for water resources, it would be remarkable to contribute to a sustainable desalination solution amid the global water crisis.”
This groundbreaking research was funded by the U.S. Department of Energy and utilized NSF-supported X-ray facilities at the University of Pennsylvania’s Materials Research Science and Engineering Center. The research team has also sought patent protection for their innovations through U-M Innovation Partnerships.
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