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Comparison of the Cake Layer Removal Options during Determination of Cake Layer Resistance (Rc) in the Resistance-In-Series Model

The resistance-in-series (RIS) model should be used cautiously, particularly in the experimental determination of the cake layer resistance (Rc) which is determined by calculation of a series of flux data that are obtained empirically before and after removing the cake layer on the membrane surface. However, the calculated Rc values are very dependent upon the cleaning methods used for removing the cake layer. Therefore, this study investigated how the various cleaning methods influence the determination of Rc. Four different cleaning methods were used: water rinsing in a shaker, manual water rinsing, ultrasonication, and sponge scrubbing. For the hydrophilic membrane, sponge scrubbing removed the cake layer completely, whereas the other methods showed removal efficiencies ranging from 79% to 99%. For the hydrophobic membrane, none of the options achieved complete cake layer removal. In addition, sponge scrubbing was not the best option for cake removal, indicating that even a method with the potential to completely remove the cake layer on a specific membrane is not universal for every kind of membrane. Consequently, a standardized method for cake layer removal to determine cake resistance (Rc) is needed for correct interpretation of the fouling phenomena with the RIS model.