How cake enhanced concentration polarization can decrease the membrane resistance

M. Keller*, C. Melang, S. Panglisch, University Duisburg-Essen, Germany

Colloidal fouling (cake layer formation) and the related increase in the hydraulic resistance is, besides biofouling, one of the main causes of energetic performance loss in membrane based desalination processes. Although this loss is economically highly relevant, physicochemical mechanisms behind the fouling related increase of hydraulic resistance are still poorly understood. Relevant interactions between simultaneously occurring membrane phenomena like concentration polarization (CP), surface charge screening, and coupled fluxes through membranes are insufficiently investigated. This particularly applies to membranes with only partial salt rejection like nanofiltration (NF) or in parts brackish water reverse osmosis (BWRO) membranes as the salt can intrude into the membrane material causing a change of the membrane resistance.

One important reason for that circumstance is the lack of differentiated experimental methods by means of which the measured overall hydraulic resistance (or its change) could be explicitly attributed to a specific type of resistance. The derivation of such relationships is highly complex since the formation of a cake layer, with its associated hydraulic resistance (RF), also influences the resistance of the concentration polarization layer (RCP) and of the membrane (RM) by a variety of potentially unknown coupling mechanisms. Therefore, the measured fouling related increase of the overall hydraulic resistance is not necessarily equivalent to RF but may also be due to associated variations of RCP and/or RM.

Within the performed study innovative experimental methods are applied to achieve a differentiated quantitative assessment of cake layer related resistance mechanisms. Cross-flow experiments showed that...

Session: M4 - Short Oral + Poster Presentations
Day: 14 March 2018
Time: 14:45 - 16:45 h

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