Charge effects on inorganic membrane performance in a cross-flow microfiltration process

Cross-flow microfiltration experiments were performed with 0.5 mu m silica particles using an inorganic membrane of 0.2 mu m pore size. We analysed how several physico-chemical factors, such as solution pH, salt concentration, and valency of the salt influenced permeate flux and fouling tendencies. The electrostatic properties of silica particles (feed suspension) and alpha-alumina particles (active layer of the membrane) were characterised by performing zeta potential measurements. It was found that the permeate flux is dependent on the surface charge of the suspended particles and possibly dependent on the surface charge of the membrane. High permeate fluxes are obtained at high pH and low salt concentration. Under these circumstances the repulsion between the silica particles is strong. In contrast, low filtration fluxes are measured at high salt concentration, low pH, and with a CaCl2 electrolyte, i.e. when the surface charges are weak and in the presence of specific cations. The net energy of interaction between the charged surfaces involved in the microfiltration process was calculated using the DLVO theory. This gave qualitative arguments for the explanation of the observed changes in the permeate flux. (C) 1998 Elsevier Science B.V.