PERFORMANCE OF PARTIALLY PERMEABLE MICROFILTRATION MEMBRANES UNDER LOW FOULING CONDITIONS

Controlling the onset of fouling and concentration polarization is cri tical in many membrane operations, particularly in the bioseparation a rea. By using stepping and constant flux experiments, the fouling thre shold or 'incipient fouling' region was studied for various microfiltr ation membranes, pH's, and bulk concentrations using bovine serum albu min. Experiments were conducted to try to decouple effects such are po rosity and pore size on incipient fouling by using a combination of tr acked etched and polyvinylidene difluoride membranes. Changes in prote in transmission and wall concentrations near the fouling threshold wer e also compared across these membranes. while porosity determined the fouling rate after the exceeding the fouling threshold, pore size appe ar to be an dominant factor in determining level of the fouling thresh old itself. The effect of pH also supports the hypothesis that the rej ections are initially dominated by membrane-solute interactions but ar e subsequently modified by protein adsorption to the surface as the wa ll concentration increases. Repulsive forces between membrane and solu te allow greater rejection (greater wall concentration) to be maintain ed without fouling but did not increase the critical flux substantiall y. Attractive electrostatic forces allow greater passage of solute (lo wer wall concentration), but the protein adsorption soon dominated and the onset of fouling occurred much more quickly. Using a conventional concentration polarization model, analysis of the results indicates t hat the onset of fouling is occurring at a relatively low wall concent rations. (C) 1998 Elsevier Science B.V. All rights reserved.