A critical flux to avoid biofouling of spiral wound nanofiltration and reverse osmosis membranes: Fact or fiction? |
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Authors: | JS Vrouwenvelder JAM van Paassen JMC van Agtmaal MCM van Loosdrecht JC Kruithof |
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Institution: | 1. Wetsus, Centre of Excellence for Sustainable Water Technology, P.O. Box 1113, 8900 CC Leeuwarden, The Netherlands;2. Delft University of Technology, Department of Biotechnology, Julianalaan 67, 2628 BC Delft, The Netherlands;3. Vitens, P.O. Box 1090, 8200 BB Lelystad, The Netherlands;4. Evides Industriewater, P.O. Box 4472, 3006 AL Rotterdam, The Netherlands;5. PWN Water Supply Company North Holland, P.O. Box 2113, 1990 AC Velserbroek, The Netherlands |
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Abstract: | The relation between biofouling and membrane flux in spiral wound nanofiltration and reverse osmosis membranes in drinking water stations with extensive pretreatment such as ultrafiltration has been studied. The flux – water volume flowing through the membrane per unit area and time – is not influencing the development of membrane biofouling. Irrespective whether a flux was applied or not, the feed spacer channel pressure drop and biofilm concentration increased in reverse osmosis and nanofiltration membranes in a monitor, test rigs, a pilot scale and a full-scale installation. Identical behavior with respect to biofouling and feed channel pressure drop development was observed in membrane elements in the same position in a nanofiltration installation operated with and without flux. Calculation of the ratio of diffusive and convective flux showed that the diffusive flux is considerably larger than the convective flux, supporting the observations that the convective flux due to permeate production is playing an insignificant role in biofouling. Since fouling occurred irrespective of the actual flux, the critical flux concept stating that “below a critical flux no fouling occurs” is not a suitable approach to control biofouling of spiral wound reverse osmosis and nanofiltration membranes. |
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Keywords: | Flux Critical flux Biofouling Biofilm Feed spacer channel pressure drop Nanofiltration Reverse osmosis Water treatment Drinking water |
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