It sounds promising: salty or polluted water is pressed through a membrane to become drinkable. But there are still technical difficulties that prevent the worldwide breakthrough. Researchers are now working on a solution.
According to UNICEF, more than two billion people worldwide do not have regular access to clean water. That is why research is being carried out worldwide on technologies that could improve the situation. One beacon of hope is microporous polymer membranes. With them, water can be freed from even the finest distributed and dissolved pollutants in order to make it drinkable. And they can desalinate seawater without having to heat it to 100 degrees.
Volkan Filiz’s department at the Helmholtz Center Hereon in Geesthacht is investigating such membranes. In principle, they work like a sieve and a magnet at the same time: “If we use them to filter polluted water, bacteria and viruses are retained because of their size while the water slips through,” explains Filiz. For many pollutants in water, the right materials and pore sizes are known to filter them out. Water can also be effectively freed from oil with polymer membranes by using oil-repellent substances.
Membranes for the treatment of salt water into drinking water are not porous. They are as dense as cling film, but still contain nanometer-sized gaps through which the small water molecules can fit, whereas salts cannot. “To do this, however, you have to press the water through the membrane with a lot of pressure,” admits Filiz.
Nevertheless, the energy consumption is lower than with conventional seawater desalination, for which the water is distilled with heat and the water vapor is collected. “We are currently looking for the most energy-efficient combination of membrane and distillation processes,” says Filiz. This so-called membrane distillation then works in principle like a Gore-Tex jacket: it does not let water through, but the water vapor produced by heat does.
A main reason why such membranes have not long been established worldwide is their short shelf life. Wherever they are used as a water filter, a biofilm forms over time that decomposes them. “Reducing this so-called fouling is one of our most important research areas,” says Filiz. The aim is to increase the service life of the membrane and thus improve cost-effectiveness.
There are high hopes for polydopamine here. This is the natural glue that allows mussels to stick to rocks underwater. Applied to a membrane, it has a hydrophilic effect – it likes to interact with water, but repels foreign substances.
In order to develop optimal filters for a wide variety of purposes, researchers must have a precise understanding of the interfacial effects between the polymers and the water. Last but not least, this requires investigations at the atomic level, such as those offered by the large-scale research facilities of the Helmholtz Association.
Research on this is to be bundled in a new center that is unique in the world: together with partners from all over Europe, DESY is planning to build the Center for Molecular Water Science (CMWS). In an interdisciplinary manner, it is intended to illuminate the topic from a wide variety of disciplines: physics, biophysics, medicine, climate research, astrochemistry, environmental technology.
“Water is one of the key issues for the future,” says Anders Nilsson of Stockholm University, one of the world’s most renowned water researchers. “The center will enable us to decisively deepen our knowledge of this.”
Read more: The article “Water – the strangest liquid in the world” first appeared on helmholtz.de.
(This article was first published on Saturday, August 27, 2022.)
