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Capillary nanofiltration (NF) enables surface water to be treated in a single step to produce high-quality permeate.Trail studies show that a stable operation is achievable using capillary NF without pretreatment (in other wordsdirect NF). The capillary NF membrane module combines the favorable cleaning properties of capillaryultrafiltration membranes with the favorable separation properties of NF membranes. The direct use of the NFprocess is referred to as "direct capillary NF" (DNF).Since June 2000 the drinking water company Vitens is carrying out several feasibility studies on capillary NF forsurface water treatment. The first three years of research on capillary NF were focussed on a stable productionprocess using a pilot installation with a single 3 inch or 4 inch membrane module. During this research periodseveral cleaning regimes were investigated. The most effective chemical cleaning procedure (within the rangeindicated on the membrane data sheet) showed to be subsequently soaking with Hsub2/subOsub2/sub, HCl and NaOH.In August 2003 a fully-automated pilot installation with two 8 inch capillary NF modules was installed. The aim wasto achieve a long term process stability with respect to seasonal fluctuations in feed water quality. The resultsare very promising, i.e. flux: 25 - 30 l/m2.h, recovery: 75%, TMP: 2,5 - 4,5 bar and Membrane Transfer Coefficient(MTC): 12 - 8 l/m2.h.bar at 20 degrees Celsius.For the second semester of 2004 the objective of the investigation with DNF was also the post-treatment and thenecessity of double barriers. So the DNF-permeate was treated by granular activated carbon (with short contacttime of about 8 minutes) and UV-disinfection. After these treatments not only European Drinking Water Standardsare fulfilled, but also the more stringent Vitens drinking water standards are achieved. Includes 4 references, tables, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 13File Size: 1 file , 620 KB