Characterization of a hollow-fiber ultrafiltration membrane and control of cleaning procedures by a streaming potential method

Polysulphone (PS) hollow-fiber ultrafiltration membranes were characterized with streaming potential measurements. The effects of pH values, ionic strengths and valences have been studied. The isoelectric points (IEPs) of the membranes were experimentally determined from streaming potential coefficients variations with pH values at a given ionic strength (0.001 mol/L). The IEPs in different media (NaCl, KCl and CaCl2 solutions) are, respectively, about 2.9±0.1, 2.9±0.1 and 3.5±0.1. This shows that the higher the valences are, the higher the IEPs are. In order to study the adsorption with colloidal hydroxide and the impact of cleaning procedures, the membranes were used to filter respectively 0.001 mol/LCuCl2, FeCl3 and AlCl3 solutions at pH 6.8. The adsorptions of the membranes measured by adsorption percentages are sight and seem to be primarily on the surface of the membranes. The streaming potential coefficients and IEPs of all adsorbed membranes are more positive compared to the clean membranes. The changes of streaming potential coefficients increase with increasing the adsorptions. Simultaneous streaming potential and flux measurements were used to evaluate the efficiency of the cleaning procedures. After the application of a washing procedure, the recovery of the membrane surface charge can be evaluated by streaming potential measurements. These results show that the streaming potential method is a useful tool for the characterization of the membrane surface charge and control of the cleaning procedures.