Steps of membrane blocking in flux decline during protein microfiltration

The flow decline is studied in typical experiments with dead-end microfiltration of BSA solutions (1 and 0.1 kg/m3) through Cyclopore® track-etched polycarbonate membranes (pore sizes 0.1, 0.2, 0.4 and 1.0 μm) at pH 5 and with a saline content of NaCl 0.01 M. Results are examined, within the frame of the common blocking mechanisms, interpreted here as successive or simultaneous steps of flow decline rather than as alternative possibilities of theoretical modelling for experimental data. An average deposited volume per unit of permeate volume is defined for the central steps of the flux decline, whose behaviour against the shear stress is studied. Under the conditions studied, an increase in shear stress results in a decrease in deposition, probably due to a reduction in protein-surface interaction times. The initial and final steps are also analyzed in terms of an early blockage of the smallest pores and a formation of a cake up to a limiting height, subsequently followed by the establishment of a final non zero flow.