MechSE team makes waves in water desalination
Three levels of the MechSE community came together on a water desalination research project that resulted in a recent publication in the journal Water Research X , which is the open-access mirror of the high-impact journal Water Research.
The paper is titled, “Low porosity, high areal-capacity Prussian blue analogue electrodes enhance salt removal and thermodynamic efficiency in symmetric Faradaic deionization with automated fluid control.”
Associate Professor Kyle Smith’s desalination research has been getting attention for years, as he continues his important work toward improving the world’s drinking water. The newer contributors were recent MechSE alumnus and first author Erik Reale (PhDME ’21), who has been working in Smith’s lab since 2016, and undergraduate students from a Fall 2019 senior capstone design team.
“My involvement was driven by a desire to stop climate change and provide potable water for people,” said Reale, who was initially drawn to Smith’s work due to his interest in electrochemistry. “The population continues to grow, and people need water.”
With more than half of humanity presently facing freshwater scarcity for one month during a given year, desalination of sea and brackish waters could be vital to improving and sustaining worldwide health and survival. Reverse osmosis currently comprises most of the global desalination capacity, and the process is limited to low brine concentrations that result in significant amounts of waste brine.
Smith’s work utilizes electrochemical deionization instead of reverse osmosis. The use of battery-like electrodes with high charge storage capacity contributed significantly to this project’s impressive results: 80% desalination of brackish water while consuming only 25% more energy than the minimum energy consumption possible for a thermodynamically reversible process.
X-ray CT image of the microstructure of a Prussian blue analogue electrode
fabricated by a novel heated, alkaline wet-phase inversion process developed
“Lithium-ion batteries absorb lithium, but this system contains a special kind of sodium-ion battery that can separate sodium-chloride salt from water,” Reale said. “This idea has been studied for several years but was limited by very high energy requirements to remove small amounts of salt. Recent advances have reduced energy consumption and removed much higher quantities of salt.”
Reale fabricated the electrodes used in the project by leveraging his understanding of van der Waals and electrostatic forces that act between particles in the suspensions that are used to make them. “It was exciting for me to see how Erik built on his knowledge of mechanics to create electrodes that were thicker and more conductive than other deionization work had reported in the past,” Smith said. “However, we were aware also that great electrodes are not enough on their own to desalinate efficiently. The coupling of current distributions within electrodes to saltwater convection plays an important role too.”
When Smith and Reale needed some heavy hands-on development for the auxiliary systems used to circulate water through their electrodes, they turned to some talented—albeit less-experienced—members of the MechSE community: a group of undergraduates seeking a senior capstone design project for ME 470.
“The recirculation system would have to route a purifying stream and a concentrating stream through two electrodes and periodically switch the flow as the desalination cell saturated and changed polarity,” said Lyle Regenwetter, the team’s leader who is now pursuing a PhD at MIT. “The control system, power system, tubes, pumps, valves, and code were the key design components.”
The project challenged the team to integrate fluid dynamics, electrochemistry, power electronics, controls, sensing, printed circuit board design, additive manufacturing, and numerical optimization. The different team members—Brian Dardon, Nicholas DiCola, Sathvik Sanagala, Adreet Agrawal, and Regenwetter—were each responsible for one or more of these different specialties.
Valve actuation system of the water recirculation apparatus designed by
Smith said he was impressed by the students’ dedication to the project as well as their creativity. “We gave the team a very open-ended task to complete, and they readily took ownership of it,” Smith said. “In particular, I enjoyed seeing the team come up with a solution for valve actuation that was inspired by a water bottle that was opened by biting on it. Their valves do the opposite – they use compression by a servo rotor to block flow through a tube. Beyond coming up with an elegant solution like that, I was excited to see the team gain confidence and experience in mechanical design toward a problem [desalination] that is not commonly associated with mechanical engineering.”
The US National Science Foundation (Award no. 1931659) supported this research.