The Wasserwerk des Kreises Aachen in Roetgen, Germany operates with financial help of the German Ministry for Education and Research and with scientific support of the IWW (Muelheim, Germany) a large scale membrane pilot plant. This pilot is equipped with twelve 6 m long pressure vessels resulting in a membrane area of about 1,620 m2 to produce about 150 m3/h of filtrate. The pilot plant was operated first with flocculated reservoir water as feed. The results show that this is a reasonable process especially if the backflush water of the plant is further treated with another membrane plant to achieve high overall recoveries up to 98-99%. Monitoring of membrane integrity is an important topic in this research. Every pressure vessel of the pilot can be connected to a particle counter by switching magnetic valves automatically. Corrupted fibres were detected by particle counting after about 8 month of operation. A correlation between the number of broken fibres and particle concentration in the filtrate could not be established and may not exist as it is discussed in this paper.

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