Four American students, participating in a program for high school girls interested in engineering, designed a bottle of desalinated water. The currently hypothetical device would be compact and portable and therefore could offer increased accessibility compared to existing desalination designs that mimic sweat.
Laurel Hudson, Gracie Cornish, Kathleen Troy and Maia Vollen met at Virginia Tech’s C-Tech2 program where they were given the mission to “reinvent the wheel”. Choosing to focus on the global water crisis and inspired by the straws used by hikers to purify water, they wondered if it was possible to make a bottle that produced drinking water from sea water. They reached out to Jonathan Boreyko, an associate professor in the Department of Mechanical Engineering, who was then researching synthetic trees. He agreed to help, and at the height of the Covid-19 pandemic, the group met virtually overnight to discuss their research. In the same way Ndidi EyeghelemeAs a graduate student in Boreyko’s lab, they planned and produced a model to assess the inner workings of their design.
Their design is inspired by mangroves, which use thermal and membrane-based desalination techniques to grow in salt water along shorelines and estuaries in the tropics and subtropics. It includes an inlet chamber, which users fill with salt water, connected to a reverse osmosis membrane. The water filters through the membrane into an intermediate chamber connected to a synthetic sheet. The sheet consists of a nanoporous membrane on a microporous mesh. During evaporation, the water meniscus inside the pores become concave, resulting in a negative pressure difference between the inside and the outside of the surface. This creates suction that can overcome reverse osmosis at the filter, resulting in desalination.
The group says the design has several advantages over existing work on synthetic trees. “We added a solar vane around the bottle to speed up the rate at which water flows through the filter,” says Boreyko. This would increase the sweat rate, ensuring the process is faster than previously reported devices. The bottle is intended for personal and community use by people who do not have sufficient access to drinking water; the proposed single column structure ensures the portability of the device. Its downward sweating path means it doesn’t need a power tank, which further ensures a compact design.
“Desalination technology is extremely expensive and energy intensive,” comments Onita Basu, environmental engineering expert at Carleton University in Canada. “The methodology they work in looks at desalination from a more sustainable perspective using a combination of biomimetic and nature-inspired technologies. This would result in a device that uses less energy and therefore is more durable, which is of the utmost importance in developing countries.
As the design is only preliminary, the obvious next step for the team would be to create a prototype. Building a physical device would involve addressing several challenges, including the cost of materials to ensure the device is accessible to intended users.