Selenium is an essential nutrient, especially for the thyroid and immune systems; however, insufficient or excessive amounts can be detrimental to both humans and wildlife. A research group at Washington University in St. Louis has made significant progress in eliminating selenium pollution from water, potentially enabling the safe treatment of water from agricultural ponds, mining runoff, or power plant effluent to comply with federal maximum standards.
Daniel Giammar, the Walter E. Browne Professor of Environmental Engineering and head of the university’s Center for the Environment, and his team utilized iron electrocoagulation to remove selenium from aqueous solutions in various studies. The findings of this investigation, supported by the National Association for Water Innovation in collaboration with the U.S. Department of Energy, were recently published in Environmental Science & Technology and ACS ES&T Engineering.
Eliminating selenium from water is complex due to its high solubility, according to Giammar. Iron electrocoagulation meets this challenge by producing iron-based solids with extensive surface areas. During the coagulation process, selenium chemically attaches to these surfaces. It can also be converted into another form of selenium that has a stronger binding affinity.
In one study, detailed in Environmental Science & Technology, graduate researcher Xicheng He, working in Giammar’s Aquatic Chemistry Laboratory, removed selenium using iron electrocoagulation in a flow-through reactor constructed by research partner WaterTectonics to generate various types of rust.
“We apply a current to the iron reactor, which accelerates its corrosion and produces rust faster than it typically would,” Giammar explained. “Iron can develop green rust prior to red rust, and this green rust is highly reactive. It interacts with selenium, extracting it from the water into iron-rich particles, which we subsequently filter out.”
This method eliminated over 98% of selenium by passing through the iron reactor for 11 seconds and then allowing it to settle for an hour, during which it remained securely bound within solids deemed nonhazardous.
In another study, documented in ACS ES&T Engineering, graduate student Yihang Yuan examined 15 different water chemistry combinations and the effects of electrochemical operating conditions on selenium extraction in batch reactors. By conducting tests in well-mixed and continuously monitored beakers of selenium-laden solutions, Yuan created a reaction-based model to forecast electrocoagulation effectiveness in removing selenium under varying levels of oxygen and pH.
“We demonstrated that this process is effective in relatively straightforward chemical mixtures because we wanted to focus on the impacts of pH and dissolved oxygen,” Giammar commented. “We observed success in the laboratory, making it applicable to real-world scenarios.”
Looking ahead, Giammar’s lab is expanding its focus beyond selenium.
“With our reactor and protocols established, we are exploring additional contaminants and natural organic matter, both in controlled compositions and using actual water samples,” he stated. “We didn’t create the reactor technology, but we illustrated to WaterTectonics that it could be effective in different contexts than they previously considered.”
He X, Flynn ED, Catalano JG, Giammar DE. Selenium(VI) removal by continuous flow-through iron electrocoagulation: Effects of operating conditions and stability of selenium in residual solids. Environmental Science & Technology, March 6, 2025. DOI: https://doi.org/10.1021/acs.est.4c12305
Yuan Y, Mehrotra M, He X, Flynn ED, Catalano JG, Giammar DE. Advancing selenium(VI) removal by iron electrocoagulation: Roles of water chemistry and operating conditions. ACS ES&T Engineering, April 13, 2025. DOI: https://doi.org/10.1021/acsestengg.5c00068
Funding for this research was provided by the National Association for Water Innovation, supported by the U.S. Department of Energy (DE-FOA-0001905).
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