“A membrane is like a sieve: it filters out contaminants such as bacteria, viruses, PFAS, and residues of medicines and pesticides that end up in our wastewater,” says Prof. Wiebe de Vos, who teaches in the Bachelor’s and Master’s programmes in Chemical Technology & Engineering.
His research group focuses on several types of membranes, among which is the reverse osmosis (RO) membrane. One of its applications is removing salts from seawater to produce fresh water. This method is essential in places where freshwater resources are limited and is already well established in many countries. But while desalination is necessary in some countries, the question is whether it is the smartest solution for the Netherlands.
Visual of Wiebe's research.
Desalination of the North Sea
Desalination, the process of removing salt from, typically, seawater, to produce fresh water for consumption, agriculture, or industry, requires a lot of energy. The RO membranes are currently the most energy-efficient desalination technology. “If you calculate the minimum amount of energy needed for desalination, membranes operate at only about twice that minimum, outperforming all other methods at the moment.” Besides, Dutch companies, such as Elemental Water Makers, are already powering reverse osmosis processes with solar energy.
RO membranes can also be used to filter out salt and impurities from brackish groundwater, which contains only about one-tenth the salt concentration of seawater. Because of the lower salinity, desalinating brackish water requires far less energy than treating seawater.
Not the most effective solution
Still, desalination of the North Sea isn't the most economical and environmentally friendly choice, according to De Vos. From every litre of treated seawater, about half becomes fresh water, whereas the other half retains twice the original salt concentration. This brine is typically discharged back into the sea where it could accumulate and sink to the seafloor, affecting marine and coastal ecosystems.
De Vos also points out transportation and infrastructure challenges. “If we desalinate water in Rotterdam and need to move it to Enschede, this adds cost and energy demands.” Transporting might also require pipelines, reservoirs, and monitoring systems, which are significant investments.
More sustainable options to desalination
“A lot can be done in water reuse and retention before resorting to desalination,” De Vos says. Especially in industry, there is a huge potential for water reuse. De Vos: “Water isn’t a resource we should only use once. It can be reused a number of times, and this is also more energy-efficient than desalination of seawater.”
For example, his research group has been developing novel nanofiltration membranes, which act as barriers against problematic pollutants such as PFAS and pharmaceuticals. These membranes are already being used at a pilot installation at the wastewater facility in Enschede to prevent such pollutants from entering surface waters. But the treated municipal wastewater becomes so pure that it can be reused in industry. Since those nanofiltration membranes require much less energy than the RO membranes, De Vos considers them an effective alternative to the energy-intensive desalination process.
Stepping stone to a hydrogen economy
However, there are future scenarios where the RO membranes could become indispensable. The Dutch government's plans for a transition to a hydrogen economy would increase national water demand, with some estimates suggesting about 12 million cubic metres of water per year, per 1 gigawatt. “In such a scenario, the membranes could be a promising solution for supplying the clean water required for hydrogen production,” De Vos says.
Global impact
“Our specialised membrane research group has existed for over 50 years, and it has led to many spin-offs that have become global companies, such as Pentair X-flow and NX Filtration. This is an example of how sustained scientific focus and collaboration with industry lead to technologies that could address future water scarcity,” De Vos concludes. Membranes can help meet future water demand but not through North Sea desalination alone. Alternatives such as nanofiltration membranes for wastewater reuse combined with smarter water management are part of the solution. 
The opening of the pilot installation at the municipal wastewater plant
