This article was written as part of The Michigan Daily’s investigation to better understand the risks, advancements and future of water in Michigan and beyond. Read other stories from the project here.
Researchers at the University of Michigan and Rice University developed a new method for purifying seawater that is more efficient than current techniques, according to an article published in Nature Water in January. The new technique removes boron, a contaminant found in seawater, using less energy and fewer chemicals.
High concentrations of boron can harm humans when present in drinking water and plants when present in agricultural water. In an interview with The Michigan Daily, Jovan Kamcev, one of the study’s authors and an assistant professor of chemical engineering at the University, said removing boron from seawater poses unique challenges because it passes through the membranes that separate most contaminants, making it one of the more energy-intensive parts of desalination.
“Boron is problematic because it’s very small,” Kamcev said. “It’s almost comparable to water. It’s uncharged, so it’s a neutral molecule. And so therefore any sort of electrostatic mechanism, it doesn’t really work for boron, so current membranes, they let through more boron than what you would like.”
According to Kamcev, current methods for removing boron include adding basic chemicals to make the boron larger and more charged, a process known as multi-pass high pH reverse osmosis, or using absorptive beads to bind boron and separate it, a process known as boron-selective absorption. However, these techniques are expensive and require large amounts of chemicals and energy.
Due to the high costs, the research team developed a different method to remove boron — using a membrane that is designed to trap the boron inside pores. Kamcev said the system uses a set of two electrodes to create a current, leading to the membrane having a positive charge on one side and a negative charge on the other. This process creates a basic solution capable of ionizing boron.
“When you apply this potential difference between the electrodes, this can actually cause water molecules between those two membranes to split, or to dissociate,” Kamcev said. “So one water molecule will turn into a proton, which is acidic, and one into a hydroxide ion, which is basic … so we’re essentially using electricity to make the basic solution that we need to ionize boron.”
According to Kamcev, ionizing the boron allows it to be separated from water by the electric current and allows it to attach itself to the electrode. However, other negative ions, such as chlorine, also bind to the positive electrode.
“There’s competition between boron and chloride, and some boron will attach to the electrodes, but other chloride will also attach,” Kamcev said. “You’re kind of wasting space on the electrode with chloride, and you can saturate it before you remove a substantial amount of boron, so that decreases the efficiency of the technology.”
Weiyi Pan, a postdoctoral researcher at Rice University and author of the paper, told The Daily the system overcomes this problem by using certain functional groups, collections of atoms with characteristic properties, inside the electrodes. These functional groups contain oxygen and can selectively bind boron more readily than they bind other substances, such as chloride.
“When you charge a battery, you can store electricity,” Pan said. “For our system, it’s more like you charge the system — it will selectively store boron. So during charging session, we extract boron, and the water can be collected for consumption.”
In an interview with The Daily, Debashis Roy, an assistant professor at the Indian Institute of Science who worked on the study as a postdoctoral researcher at the University, said the system’s selective design allows it to be more efficient.
“This technique was so simple but effective because we don’t use any external chemicals (in) it, so it is less chemically intensive,” Roy said. “At the same time, we don’t use high pressure or high electric current. So you can use just less than 1.4 volts of electric current, and then you can separate boron, very selectively.”
Kamcev said while the results of the study are promising, the system still needs further work before it can be implemented in large-scale creation of potable water.
“One of the key steps that we’re looking for next is to try to work with an industrial partner to try to scale this up to actually run like a larger scale system, instead of doing one in the laboratory,” Kamcev said. “Along with that, we’ll do a much more rigorous techno-economic analysis to see how much this would cost when you consider things like the cost of the materials and then the operating costs.”
Engineering junior Alexander Lourbas, public relations chair of the University chapter of the American Institute of Chemical Engineers, said the study will help inspire students who hope to make an impact through chemical engineering.
“Professor Kamcev’s innovations and the study that he accomplished really does serve as somewhat of a north star for undergraduates looking to follow in these footsteps,” Lourbas said, “For all of us under the Wolverine umbrella, there is that join culture of research excellence and innovation within chemical engineering, and this study serves as a really key cornerstone to that passion that many undergraduates have.”
According to Kamcev, this study is important because water scarcity is becoming an increasingly widespread issue due to climate change and over-consumption. Utilizing sea water Kamcev said, may be one component of addressing the problem.
“Developing technologies that can purify seawater in an energy-efficient and sort of inexpensive way is really critical,” Kamkev said. “I think we still have a lot of work to do to make these more inexpensive, to make them more efficient, so that the people that really need them throughout the world can actually have access to them.”
Daily News Reporter Nadia Taeckens can be reached attaeckens@umich.edu.
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