FOULING OF INORGANIC MEMBRANES DURING WHEY ULTRAFILTRATION - ANALYTICAL METHODOLOGY

Ultrafiltration of various types of whey was carried out through an inorganic membrane (M4 Carbosep, 20000 Da cut-off). Fouling was evaluated as a hydraulic resistance (Rf) and analysed with infrared (IR) and X -ray photoelectron ( XPS) spectroscopies, giving complementary results. Spectroscopic data are in a very good agreement with UF flux variations and Rf values: the higher the transmembrane pressure or the whey protein content, the higher the fouling protein content. Proteins are found in the bulk of the membrane as well as on its surface, their concentration being higher in the latter case, whereas the phosphate/protein ratio lies often in the range 25-45% whatever the whey type or the operating conditions. Qualitatively, phosphate organization involves at least adsorbed hydrogen-phosphates and apatite structures resulting from several interactions between phosphate, protein, calcium and membrane. Only when the pH is increased up to 6.9 does PO4 organization typically reach the apatite lattice. Its level is highest in the bulk of the membrane (4.1% relative to ZrO2), representing nearly 85% of the protein content. © 1990.