Europe has a water problem. The continent is one of the regions most affected by climate change, with average temperatures rising every summer, making freshwater an increasingly strategic resource.

According to the Water Exploitation Index Plus (WEI+), in 2022 the most severely affected countries in the EU were Cyprus (92%) and Malta (61%). Other southern member states – Portugal, Greece, Spain, Romania, and Italy – also recorded high values between 30% and 38%.

According to the European Environment Agency, one-third of the EU’s land area experienced dry spells that summer, affecting 41% of the population. As it’s unlikely summers will get any cooler in the near future, governments and researchers are exploring a few solutions to freshwater shortages. One of these, seawater desalination, has emerged as a particularly viable solution.

The procedure is pretty straightforward: salt and other impurities are removed from seawater, producing clean, drinkable water ready for use. However, the process is also not without its environmental challenges, as it generates large volumes of waste brine, a concentrated salt solution often discharged back into the sea.

To eliminate this side effect of desalination, the National Technical University of Athens is testing a new approach within the larger scope of the EU-funded WALNUT project: recovering valuable materials from brine to produce fertilisers.

At the helm of this branch of the initiative is Dr Maria Kyriazi, a chemical engineer with a PhD in electrical engineering. She is part of the Unit of Environmental Science and Technology (UEST) at the School of Chemical Engineering of the National Technical University of Athens – a group with extensive experience in wastewater treatment, resource recovery, and circular economy solutions.

Are we entering a new era of water stress in southern Europe?

Yes. We’re already seeing water availability drop across the region. Prolonged droughts, higher evaporation, and changing rainfall patterns. This puts real pressure on our water supply in summer, when tourism spikes, farms need more water, and there’s little rain.

How is Greece adapting to this crisis?

We are seeing a new effort to reuse wastewater, upgrade irrigation systems, and invest in solutions to cut down on leaks. There’s also a growing interest in circular systems to recover useful resources from wastewater. It’s probably a sign that sustainability is becoming more and more a national priority.

Which brings us to desalination. Would you still call it a “new” technology?

Well, the process itself has been around for decades. What I would say instead is that how we do it has changed. There have been a few new advances in membrane technology and energy efficiency. It is definitely a more practical and cheaper option than it used to be. However, the real challenge we wanted to tackle was brine management. Desalination produces this salty, concentrated byproduct left over at the end that’s often dropped back into the sea.

Is it bad for the environment?

It is, unfortunately. It can increase the local water salinity and temperature, and reduce oxygen levels. Also, it often comes with residual chemicals from pre-treatment and cleaning operations. The good thing, though, is that these brines also have useful elements in them.

Which brings us to the part of your work that’s connected to WALNUT.

Exactly. So, our approach, the real novelty perhaps, is that after the desalination process, we also recover crucial materials contained in these brines. Think of magnesium and potassium, for example, which can be used as fertilisers. That’s how desalination becomes part of a circular, more self-sufficient system. So, on one hand, you have high-purity water, and on the other, a source of marketable secondary raw materials.

That also ties into Europe’s fertiliser independence and food security.

Absolutely. Europe still relies heavily on imported magnesium and potassium for fertiliser production. If supply chains are disrupted, food production is immediately affected. Recovering these minerals from wastewater reduces that dependency and supports a more resilient and sustainable farming system. It also fits directly into the EU’s Green Deal and Farm to Fork strategies.

Can you walk us through how the NTUA brine treatment system works?

Sure. The system is fully modular and containerised, so it can be easily transported and set up. It includes five main steps: First, there are two precipitation units where we recover magnesium and calcium as magnesium hydroxide and calcium carbonate. Then, a nanofiltration unit removes the remaining divalent ions from the brine. After that, the process goes through two evaporation stages to crystallise sodium chloride, and finally, there’s a flotation step to separate potassium chloride – also valuable for fertiliser use.

Could this technology be deployed in small island communities, remote areas, or agricultural zones?

Absolutely. The modular, containerised design makes it easy to adapt and deploy in remote or off-grid locations.

Where is the demo unit currently operating? Has the local response been positive?

It operates in Cyprus, near a desalination facility. The island was chosen because it faces some of the most intense water stress, especially during summer. As for the local response, it has been very positive. Residents appreciate the environmental and economic benefits the system brings to their community.

Could Greece play a leading role in exporting this solution to other drought-affected parts of Europe or the Mediterranean?

Yes, I think so. Greek desalination technology providers already have a strong presence in Europe, Africa, and Asia. We have both the know-how and the track record to export solutions. Well beyond the Mediterranean.

What excites you most about this work, as a scientist and as a citizen?

The chance to turn challenges into resources. My team is committed to the idea that nothing should go to waste. As a scientist, I think it’s incredibly rewarding to see research move beyond the lab and into the real world. And as a citizen, I’m proud to help build a more sustainable and resilient future for our communities.

Cover image by u_nnjglrk13q on Pixabay

Contacts:

Project coordinator:
Francisco Corona Encinas, PhD FUNDACIÓN CARTIF - fraenc@cartif.es
Communication Manager:
Francesco Agresta, ICONS - info@walnutproject.eu

Project website: https://walnutproject.eu/
LinkedIn: WALNUT
Twitter: @walnut_project