HYDRAULIC PERMEABILITY OF PROTEIN DEPOSITS FORMED DURING MICROFILTRATION - EFFECT OF SOLUTION PH AND IONIC-STRENGTH

Protein deposits formed during membrane filtration can dramatically re duce the effectiveness of these devices. We have obtained data for the hydraulic permeability of deposits formed by the filtration of albumi n, lysozyme, ribonuclease A, hemoglobin, and immunoglobulins. The stea dy-state permeability for each of the protein deposits was minimum at the protein isoelectric pH and decreased with increasing salt concentr ation at pH both above and below the isoelectric point. The transient response of these protein deposits to an increase in solution ionic st rength consisted of an instantaneous jump in flux followed by a relati vely slow flux decline. This complex behavior was consistent with the effects of the solution environment on the protein packing density wit hin the deposit (which is determined by the balance between the interm olecular electrostatic repulsion between protein molecules and the com pressive pressure associated with filtration) and on the magnitude of the electro-osmotic counterflow associated with the streaming potentia l that is generated across the deposit. These results provide importan t insights into the physical phenomena governing the structure and hyd raulic permeability of the protein deposits formed during membrane fil tration.