Microfiltration of protein/dextran/polyphenol solutions: Characterization of fouling and chemical cleaning efficiency using confocal microscopy

Since most of the biological streams are complex mixtures of proteins, polysaccharides and polyphenols. in this paper we characterize membrane fouling caused by ternary model solutions containing a protein (BSA-FITC, 0.25 g/L), a polysaccharide (dextran-RITC, 0.25 g/L) and a polyphenol (tannic acid, 0.25, 0.5 and 1 g/L) filtered using 0.8 mu m polycarbonate membranes. Our results clearly show that the presence of tannic acid reduced permeate flux, regardless of its concentration. Though tannic acid could not be visualized under the imaging conditions used during confocal scanning laser microscopy (CSLM) analysis, its effect on membrane fouling was clear since in all analyzed membranes we detected a 8.5-17.5 mu m thick deposited cake layer that was absent when a protein/dextran solution of the same concentration was studied. The formation of protein/polyphenol and/or protein/dextran/polyphenol complexes is believed to be the main cause of external fouling and the decrease in permeate flux. A higher tannic acid concentration in the solution increased the presence of the protein inside the pores. For the highest polyphenol concentration, the fraction of pore where protein or dextran was detected (P-s) reached 100% and was maintained from the membrane surface up to 1 mu m inside the membrane. The effect of the presence of the polyphenol in the solution on dextran deposition/adsorption on the pores was less obvious than for the protein. However, for all tannic acid concentrations, there was a slight increase in P, for dextran when tannic acid was present. A study on chemical cleaning of membranes fouled with ternary solutions of BSA/dextran/tannic acid was also performed. The chemical cleaning protocol used an enzymatic detergent and water permeate flux recoveries of between 35 and 55% were obtained. (C) 2009 Elsevier B.V. All rights reserved.