EFFECT OF INTERPARTICLE ELECTROSTATIC DOUBLE-LAYER INTERACTIONS ON PERMEATE FLUX DECLINE IN CROSS-FLOW MEMBRANE FILTRATION OF COLLOIDAL SUSPENSIONS - AN EXPERIMENTAL INVESTIGATION

A systematic study on the effect of electrostatic double layer interac tion on permeate flux decline and deposit cake formation in crossflow membrane filtration of colloidal suspensions is reported. Three monodi sperse silica suspensions with diameters of 47, 110, and 310 nm were u sed as model colloids, and a tabular zirconia membrane with an average pore diameter of 20 nm was used as a model membrane. The magnitude an d range of the electrostatic double layer interactions were controlled via changes in solution ionic strength and pH. The coupling between c olloidal interactions and hydrodynamic forces was investigated by chan ging the transmembrane pressure and particle size. The results indicat e that the rate of flux decline is strongly dependent on solution ioni c strength and, to a much lesser degree, on solution pH (for the inves tigated pH range 6.1-10.0). Variations in flux decline rate with solut ion ionic strength are especially significant as the particle size dec reases. Particle cake thickness, permeability, and porosity generally increased with a decrease in solution ionic strength for a given parti cle size. For given physical and chemical conditions, the cake layer p orosity increased with decreasing particle size, while cake permeabili ty decreased with decreasing particle size. These trends are consisten t with the increased importance of double layer repulsive forces in co ntrolling the cake layer structure as the solution ionic strength and particle size decrease. Pressure relaxation experiments indicated that the particle cake layer is reversible, implying no irreversible depos ition (attachment) of silica colloids onto the zirconia membrane surfa ce. (C) 1998 Academic Press.