Cake properties as a function of time and location in microfiltration of activated sludge suspension from membrane bioreactors (MBRs)

• Characteristic parameters of activated sludge were determined by a fitting method.
• The location and resistance of skin layer were quantitatively analyzed.
• Cake properties varied sharply within the skin layer at the location of x/L < 0.2.
• The structure of cake layer was opposite to that of the asymmetric membrane.

How to determine characteristic parameters in Tiller’s power-law expressions is crucial to analyze cake properties in microfiltration using conventional cake filtration theory. In this study, these characteristic parameters of activated sludge from MBRs were determined by fitting experimental data to our proposed equation, and then cake properties were analyzed from two aspects of time and location. In addition, the relative cake resistance (Rx/Rc), and the resistance and location of the skin layer under different operating conditions were quantitatively analyzed by our developed equations. Results indicated that variations of cake properties with time were inconspicuous, while cake properties varied sharply over location until the relative thickness (x/L) reached 0.2. The cake consisted of a skin layer (at the location of x/L < 0.2) below a loose layer, which was opposite to the structure of asymmetric membrane. More than 70% of cake resistance concentrated in the skin layer whose thickness was only 20% of cake thickness. Predictions of permeate flux determined by obtained cake properties showed good agreement with experimental data.

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