Particle deposition during membrane filtration of colloids: transition between concentration polarization and cake formation

• Published in: Journal of membrane science Vol. 125; no. 1; pp. 109 - 122
• Main Authors: Chen, V, Fane, A.G, Madaeni, S, Wenten, I.G
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05-03-1997; Elsevier
• Subjects: Applied sciences; Chemical engineering; Concentration polarization; Critical flux; Exact sciences and technology; Fouling; Membrane separation (reverse osmosis, dialysis...); Microfiltration; Ultrafiltration; Critical flux; Microfiltration; Fouling; Ultrafiltration; Concentration polarization; Critical property; Sulfone polymer; Polymeric membranes; Cellulose hydrate; Experimental study; Silica; Transport process; Rejection; Membrane separation; Colloidal suspension; Vinylidene fluoride polymer; Membrane filtration; Deposit formation; Filter cake
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/S0376-7388(96)00187-1

The transition from concentration polarization to cake formation has been studied for the membrane filtration of colloidal silica by imposing flux and observing the system response. A critical flux (
J
crit) has been measured, below which transmembrane pressure drop, Δ
P, is stable for increasing and decreasing flux. The flux–pressure profiles for operations below
J
crit show little (for MF) or negligible (for UF) hysteresis. Above
J
crit the pressure has a period of instability for increasing and decreasing flux, and there is significant hysteresis. It appears that once
J
crit is exceeded, the colloids in the polarized layer form a consolidated cake structure that is slow to depolarize and which reduces the flux. Evidence for cake deposition was obtained from electron micrographs. The depolarization can be increased by crossflow, by washing, and increasing pH. It was observed that the slow incrementation of flux to a given high value can result in significantly lower Δ
P than the direct application of that flux. These differences are ascribed to formation of a stagnant, highly concentrated layer near the membrane surface due to consolidation and aggregation of solute resulting from very rapid flux increases.