Novel Fouling Repellent Metallic Microsieves Offer Hope for Clean Water in Developing Countries and Conflict Zones

Advanced nano-engineered membranes for water purification have been developed at Fraunhofer UMSICHT, Process Technology (Oberhausen, Germany) by researchers Ilka Gehrke and Volkmar Keuter.

In 2030, 47% of world population will be living in areas of high water stress (UN World Water Development Report 3, 2009). From the global water shortage a growing need for novel, more efficient and cost saving water purification methods is emerging. In both developing and industrialized countries a growing number of contaminants like micropollutants (e. g. endocrine substances) are entering water supplies. Conventional water decontamination processes based on oxidizing chemicals like ozone or chlorine consume a high amount of chemical agents and, furthermore, can produce toxic by-products. A more promising water cleaning method is represented by membrane technology which uses few chemical substances and prevents contaminants from passing through the membrane with water molecules. However, membrane processes are characterized by a high tendency to fouling resulting in drastically flux decrease.

The adaption of highly advanced nanotechnology to traditional process engineering offers new opportunities for the intensification of water processes. In Kreuter and Gehrke’s approach the focus is on the application of nanocoating procedures to membrane processes in order to reduce the fouling potential of membranes and increase the filtration capacity.

Nanocoating methods based on biocide and photocatalytic substances like titanium dioxide and silver are applied in order to functionalize membranes. For producing suitable membranes novel molding processes were utilized. Specific experimental set-ups at laboratory scale for measuring permeate flux, pressure loss and photocatalytic as well as biocide effects were mounted.

Novel metallic microsieves at (critical dimension) CD-scale, including a homogeneous pore size distribution and higher robustness, have been developed and tested. They feature an enormous permeate flux. In order to maintain the high permeate capacity, currently, fouling repellent nanocoatings consisting of photocatalytic titanium dioxide are applied to the membrane surface. The coatings are characterized by a high adhesion to the metallic membrane material. The coating process can be exactly controlled, so the very precise pore geometry is preserved and the holes are kept unblocked from coating material.

The novel fouling repellent metallic microsieves are to be implemented in compact and flexibly adjustable membrane modules particularly for producing potable water but also for the post-treatment of waste water. Due to their high robustness and easily handling among others decentralized plants, e.g. for conflict areas and developing countries are possible.

Results were reported in the proceedings of  "EuroNanoForum 2009, Nanotechnology for Sustainable Economy: European and International Forum on Nanotechnology."