According to the WHO / UNICEF Joint Monitoring Programme for Water Supply and Sanitation, the lack of potable water in many regions is one of the major challenges we have to face in the 21st century" .

However, this is not a problem of water scarcity in general, but the quality of the available water: less than one percent can be considered as potable. On the other hand, as more than 25% of the world’s population live closed to the seashore the desalination of seawater may provide a solution to face the lack of clean and fresh water to billions of people. The separation of the dissolved ions (mainly sodium chloride) from the water is therefore of great interest for potential applications.

This idea is addressed by M. Wilhelm et al. in their recent communication in Macromol. Rapid Commun. They use poly(acrylic acid) hydrogels which due to their hydrophilic acidic groups are soluble in water and take up water like a sponge because of the polymer network structure. In contrast to natural or synthetic sponges, these materials can absorb more than 100 g water per 1 g polymer network and are therefore called super-absorbers. As the polymer already contains ionic groups that are fixed on the strands, these charges will repel the ions in the sea water. Thus the absorbed water will possess a lower salt concentration than the natural sea water concentration. After this separation in a second step the water has to be recovered from the polymer network. The authors employ mechanical pressure to squeeze out the water like from a sponge. In optimal cases this will be fresh water.

In the present publication the authors prove the applicability of their concept by deswelling experiments using a self-constructed apparatus combined with salt concentration analysis. They investigate some parameters that can be tuned to improve the process, e.g the charge density on the polymer backbone or the crosslinking density of the network.

This idea, as intriguing as it is, is still a long way from commercial application due to its energy and time consumption in comparison to several desalination methods already applied nowadays. However, the authors continue exploring the possibilities for seawater desalination which arise from this new concept.

M. Wilhelm, Macromol. Rapid Commun. 2010 ; DOI: 10.1002/marc.201000058