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Journal of Membrane Science
Vol. 475, 2015; Pages: 131146

Biofouling removal in spiral-wound nanofiltration elements using two-phase flow cleaning

Y. Wibisonoa, K.E. El Obied, E.R. Cornelissen, A.J.B. Kemperman, K. Nijmeijer

University of Twente, Membrane Science and Technology, MESA+ Institute of Nanotechnology, Faculty of Science and Technology, P.O. Box 217, 7500 AE Enschede, The Netherlands

Abstract

Biofouling has detrimental effects on the feed channel pressure drop and the permeate flux in high-pressure membrane processes such as NF and RO. Two-phase flow cleaning is a chemical-free technique that is able to remove such biofilms. This paper presents a study into the effects of the gas/liquid ratio, feed spacer geometry, applied pressure and liquid velocity on the efficiency of two-phase flow cleaning in spiral-wound nanofiltration elements. A high-speed camera, optical coherence tomography and scanning electron microscopy were used to study biofouling and its removal. Our results show that two conditions must be met to ensure that a sufficiently high shear force is applied to biofilms on membrane and spacer surfaces. A good bubble distribution in the channel is the first requirement. While it is mainly the structure of the feed spacer that controls bubble flow and bubble size, a minimum gas/liquid ratio of 0.5 is necessary to achieve a good bubble distribution. The second condition is the use of a sufficiently high liquid velocity during cleaning. The bubble velocity was found to be 3.5–5.5 times as high as the used liquid velocity, and responsible for a marked improvement in the flux recovery.

Graphical abstract

Key words: Biofouling; Nanofiltration; Spiral-wound membrane; Two-phase flow cleaning; Optical coherence tomography

 
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