Microfiltration membrane resistance control

Blatt WF, Dravid A, Michaels AS, and Nelson L. Solute polarization and cake formation in membrane ultrafiltration Causes, consequences and control techniques. In Membrane Science and Technology, ed., Fhnn JE, Plenum Press, New York, 1970, pp. 47-97. 40. Blanpain-Avet P, Doubrovine N, Lafforgue C, and Lalande M. The effect of oscillatory flow on crossflow microfiltration of beer in a tubular mineral membrane system—membrane fouhng resistance decrease and energetic considerations. J. Membr. Sci., 1999 152(2) 151-174. 

Two process modes, namely, dead-end and cross-flow modes, are widely used for microfiltration (14). For the dead-end mode, the entire solution is forced through the membrane. The substances to be separated are deposited on the membrane, which increases the hydraulic resistance of the deposit. The membrane needs to be renewed as soon as the filtrate flux no longer reaches the required minimum values at the maximum operation pressure. This mode is mostly used for slightly contaminated solutions, e.g., production of ultra-pure water. For the cross-flow mode, the solution flows across the membrane surface at a rate between 0.5 and 5.0 m/s, which prevents the formation of a cover layer on the membrane surface. A circulation pump produces the cross-flow velocity or the shear force needed to control the thickness of the cover layer. The system is most widely used for periodic back flushing, where part of the filtrate is forced in the opposite direction at certain intervals, and breaks up the cover layer. The normal operating pressure for this mode is 1-2 bars. 

The formation of ceramic membranes for microfiltration, ultrafiltration or nanofiltration by association of various granular layers is now a common procedure [10]. Each layer is characterized by its thickness, h, its porosity, 8, and its mean pore diameter, dp. These parameters are controlled by the particle size, d, and the synthesis method. Each layer induces a resistance which may be predicted through the classical Carman-Kozeny model ... 

All these examples clearly indicate that not only is the membrane performance important in microfiltration but particularly the chemical and thermal resistance of the materials used. Furthermore, the control of fouling is extremely important as well and this is discussed further in chapter VIL... 

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