How polymers and natural temperature variations serve to produce clean drinking water

Is there a way to obtain fresh water from seawater without employing conventional desalination techniques? A team led by Professor Sebastian Seiffert of the Department of Chemistry at JGU has developed a very promising approach to dealing with this important question. The HydroDeSal concept uses a hydrogel that reacts to changes in temperature. Once it gets cooler in the evening, the hydrogel draws water from the sea, already rejecting the salt, and then releases clean, salt-free drinking water during the day when temperatures rise. The application of this strategy is now to be made ready for the market.

Many people do not have reliable access to clean drinking water, despite the fact that our planet is rich in water. Most of it – about 96 percent – is found in seas and oceans. Because of its high salt content, however, it cannot be used directly as fresh water. This is the starting point of the HydroDeSal concept developed by Professor Sebastian Seiffert's team at the Department of Chemistry of Johannes Gutenberg University Mainz (JGU) together with cooperation partners in the Middle East. "We are exploring the use of a thermoresponsive hydrogel that is capable of producing fresh water from seawater in response to the natural temperature fluctuations between day and night." The process has been shown to work reliably on a laboratory scale. The team is now looking for industrial partners willing to help make the idea viable for mass production. "We need commercial associates to take our approach to market and turn it into a product," says Seiffert.

But how does HydroDeSal work? Dr. Amir Jangizehi, a colleague in Professor Seiffert's team, explains the process with the help of the experimental setup in the lab. The focus is on hydrogels made of polymers. We actually find them in everyday products, such as in baby diapers, because they can absorb large amounts of moisture. In the case of HydroDeSal, however, the researchers are employing a specific class of these substances known as thermoresponsive polymers. In addition to performing a specific function, they can also change their physical properties, and thus their behavior, in response to changes in ambient temperature. For desalination, the researchers use a polymer that absorbs water during the cooler nighttime hours while retaining any salts present. When it warms up during the day, the swollen hydrogel releases the absorbed desalinated water. HydroDeSal uses this cycle to provide fresh water. By comparison, today's large-scale desalination plants use energy-intensive evaporation and reverse osmosis processes.

"Our goal is to replace these processes with a sustainable and self-sufficient system that requires little additional electrical power to be supplied, for example, by solar energy," adds Sebastian Seiffert. People living near coastlines without access to drinking water infrastructure supplied by conventional desalination plants would benefit most. According to the researchers, it should be possible to scale the HydroDeSal system to meet the drinking water needs of small settlements and villages – and thus contribute to finding solutions for the increasing global water shortage. "A local solution to a global challenge," says Seiffert, Professor of Physical Chemistry of Polymers at JGU.

The HydroDeSal research project was funded by the German Federal Ministry of Education and Research (BMBF) starting in 2021 as part of its Middle East Regional Water Research Cooperation Program (MEWAC), which aims to improve water security in the region. Almost all countries in the Middle East suffer from a rapidly increasing water shortage and are severely affected by water stress, which is increasing due to global climate change. According to Seiffert, the trustful collaboration with regional partners fits in perfectly with the project's local focus. "The researchers there have made important contributions to the development of the membrane technology required for our project. Since the site is only a few minutes' walk from the sea, we were able to test our system under real conditions." Amir Jangizehi established contact with the project partners in the Middle East. The multinational project team included polymer scientists, chemical engineers, and membrane technology experts.

For Sebastian Seiffert, the HydroDeSal concept needs to be seen in the context of a wider problem – that of climate change. This issue has been a major concern of his since 2019. At the beginning, he contributed to the Lecture for Future series, explaining climate change from the physicochemical perspective. "I was shocked as I delved deeper and deeper into the subject. It was then that the 'climate penny' finally dropped for me," Seiffert remembers in retrospect. As a result, he now calls on the natural sciences to embark on the necessary research to find solutions. "It was Albert Einstein who said: 'Those who have the privilege to know have the duty to act'," emphasizes Seiffert, for whom HydroDeSal is a matter close to his heart. After all, it is evidence of how an appeal to science can result in an application suitable for general use.

Related links

• Research group of Professor Sebastian Seiffert at the JGU Department of Chemistry
• HydroDeSal project

Read more

• JGU Magazine: "Soft matter – materials of the future" (23 July 2024)
• press release "From theory to application: DFG-funded Research Unit 2811 to develop switchable polymer gels" (17 Oct. 2022)
• press release "Researchers of Mainz University involved in federally funded seawater desalination project in the Persian Gulf" (9 June 2021)