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Germany : Ultrafiltration creates clear conditions

August 9, 2014

Seas and oceans are the biggest water reservoirs on Earth. Since decades sea water is turned to drinking water by desalination in large scale. In Ghana, West Africa, a modern desalination plant is currently being established to produce up to 60,000 cubic meters of drinking water per day enough to supply half a million people. In this plant ultrafiltration membranes made by the BASF subsidiary ingeŽ play an important role: They are used to pretreat the salt water in order to optimize the actual desalination and to protect the downstream salt filters from contamination. These salt filters operate according to the reverse osmosis principle hereby the water diffuses as individual molecules through the sensitive membrane. As high pressure of up to 80 bar is required for this process, the pre-purification by means of ultrafiltration additionally contributes to the limitation of the energy input.

The water taken out of the sea is forced under pressure through the very fine-pore MultiboreŽ membranes and can pass through them, while undesired substances such as sand, clay, algae and even pathogenic germs are intercepted. At first glance, the ultrafiltration membranes look like thin white tubules, but the cross-section reveals their complex inner life: The fiber contains seven capillaries into which the raw water runs. The walls of the capillaries have tiny pores with a diameter of about 20 nanometers this is 500 times thinner than a filament of a spider's web. All the particles larger are retained here by the membrane. Only the purified water passes through the pores into the plastic fiber and emerges again on the outside of the fiber.

Production of the membranes requires extensive know-how and experience. The challenge is to create pores during the production process that are small enough and evenly distributed over the membrane surface, explains Dr. Nicole Janssen, Laboratory Team Leader at Performance Materials Research. Together with her team, she is optimizing the conditions and the starting material from which the membrane fibers are manufactured: the BASF plastic UltrasonŽ E, a polyethersulfone. We can now adjust the UltrasonŽ solution and the process so accurately that the membranes offer dependable filter performance.

For the filters to work reliably in practice, however, not only the size and distribution of the pores have to be correct, the fibers also have to be resistant. This is ensured by the honeycomb structure inside the fibers designed by the experts of the BASF subsidiary ingeŽ. The arrangement of the seven capillaries in the supporting structure makes the fiber mechanically stable and thereby resilient, explains Martin Heijnen, Head of Membrane Development at ingeŽ, who adds: This protects the membranes against fi ne cracks through which otherwise bacteria or viruses could pass.

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Source: TendersInfo (India)

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