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High fluxes for water filtration

Sabine Paulussen from the NANOPUR project spoke to research*eu results magazine about the project's novel membrane solution for water filtration.

Combine water scarcity with an ever growing population, and society is faced with a major question: how can we increase the productivity of water filtration systems while maintaining the highest standards for drinking water purity? The NANOPUR project is offering a solution in the form of a novel membrane, which should be rolled out within the next two to five years. As European citizens, our daily use of running water has become increasingly mechanical. Not only do we drink water from the tap in all confidence, but we never really question its origins or quality. So far, available technologies have been satisfying in this regard: behind the scenes, filtration and sanitation processes clean water to remove traces of micro-pollutants and viruses, so that used water can become drinkable once again. Thanks to these processes, which include membrane-based filtration, the likes of pharmaceutical products, endocrine disrupting compounds, pesticides and industrial chemicals can safely be extracted from treated water. But are current technologies really efficient? According to Sabine Paulussen, coordinator of the NANOPUR (Development of functionalized nanostructured polymeric membranes and related manufacturing processes for water purification) project, concentrations of several micropollutants in surface water are still exceeding ‘Human health limits’ (HHL), indicating the need for robust drinking water treatment to safeguard consumers from potential health risks. Another problem lies in membrane fouling: Today, membrane processes rely on size exclusion. The pores of filtration membranes are very narrow, which means that the water fluxes through the membrane are very limited. This means the filtration process is not as efficient as it could be, and with society’s growing needs for fresh water and increased water scarcity, these limitations can become a problem. With the aim of tackling these issues, the NANOPUR project is developing artificial membranes which combine the selectivity of biological membranes with the mechanical strength and productivity of state-of-the-art artificial ones. The project promises selectivity vis-à-vis pathogens of up to 99.99999 % and towards micropollutants of up to 99 %, along with higher permeability and reduced energy consumption. Sabine Paulussen explains what makes the new membranes so innovative, and discusses future steps towards their commercialisation. What are the main objectives of the project? The NANOPUR project aims to develop nano-structured and nano-functionalised membranes able to remove viruses and organic micropollutants from water, either for ‘Point of entry’ (POE) or ‘Point of use’ applications (POU). The key concept is to overcome the frustration arising from the seemingly unbreakable linkage between increased retention and lowered water flow through the membrane when it comes to producing safe and pure drinking water. The membranes that are being developed under the NANOPUR project are characterised by improved retention of viruses and micropollutants, while high fluxes can be applied and maintained by reducing the fouling propensity of the membranes. For this aim, nano-structured, low-fouling membranes are being developed by bottom-up synthesis, for a better control of porosity, pore size distribution, hierarchical orientation of the pores, surface roughness and surface energy. Simultaneously, ligands for supramolecular recognition, in particular ‘Molecularly imprinted polymers’ (MIPs) are being developed and immobilised onto the newly developed membranes for an effective capture of viruses and micropollutants. What do you expect in terms of performance compared to existing technologies? Today, membrane processes (reverse osmosis) are already applied for the removal of micropollutants and viruses, but they rely on size exclusion. Given the small size of viruses and especially organic micropollutants, membranes with very narrow pores have to be used, giving rise to high process pressures and low water fluxes through the membrane. In addition, frequent cleaning procedures are needed. The NANOPUR concept is providing an efficient solution to overcome these problems. Moreover, we are aiming for energy consumption 500 times lower than that of reverse osmosis processes, for a similar retention of viruses and micropollutants. What were the main difficulties you faced in the development of these membranes? The main difficulties were related to increasing the water flux through the membranes while maintaining their pore size and the connection between the membrane and the affinity ligands/MIPs. Both issues were at least partly tackled by applying atmospheric plasma technology to modify the surface energy of the membranes, including their pore network, and to generate functional groups at the surface. The latter can serve as anchorage points for MIP immobilisation. How promising are the results obtained so far? We actually managed to immobilise MIPs onto functionalised membranes while showing very good retention of some specific micropollutants. What’s more, these results are obtained without the need to apply any pressure. When do you expect this technology to hit the market? The project ends in April 2015, and we have high hopes of seeing the technology commercialised within the next two to five years. What are the next steps for the project, and do you have any follow-up plans after its end? Over the next six months, we will focus on testing the newly developed membranes at pilot scale. The membranes will be used for the treatment of realistic waste waters contaminated by micropollutants. For further information, please visit: NANOPUR