DETERMINATION OF OSMOTIC-PRESSURE AND FOULING RESISTANCES AND THEIR EFFECTS ON PERFORMANCE OF ULTRAFILTRATION MEMBRANES

A study was made of the effects of material and geometric properties of ultrafiltration (UF) membranes on flux decline due to concentration-polarization (osmotic pressure) and adsorption (fouling) resistances. UF experiments with solutions of beta-lactoglobulin and bovine serum albumin on commercial membranes of poly (vinylpyrrolidone)-coated polycarbonate (PC) and regenerated cellulose (RC) were carried out. A three-stage experimental strategy based on an osmotic pressure-adsorption model was used to separately determine the effective hydraulic membrane resistance, osmotic pressure, and fouling resistance. By a normalization procedure, the performance of membranes with varying material and geometric characteristics could be compared and evaluated in terms of the extent of flux reduction individually due to concentration-polarization and fouling. Under all the conditions studied, the total flux reduction for the PC membrane was mainly controlled by the fouling resistance and for the RC membrane by the osmotic pressure build-up due to concentration-polarization. The effect of bulk protein concentration, transmembrane pressure, crossflow velocity, pH, and NaCl concentration on the individual, relative contributions to flux reduction by osmotic pressure and fouling were found to depend on membrane material properties.