Electro-microfiltration of Colloidal Suspensions

Abstract

Crossflow microfiltration experiments using polymethyl methacrylate (PMMA) colloidal suspensions by a flat-channel electro-filter were performed to investigate the effects of electric field strength applied and the surface properties of particles, such as zeta potential and electric double-layer thickness, on the filtration rate, average specific cake filtration resistance, and cake porosity. Mathematical models for relating the quasi–steady state filtration rate and the separated distance between deposited particles on cake surface to the operating parameters were also presented. Both the experimental data and the theoretical model indicated that the filtration rate–electric field strength dependence was linear when the filter was operated in regions under the critical electric field strength. However, when the electric field was greater than the critical strength, the filtration rate was obtained by the addition of the electro-osmotic flux and the hydraulic permeate flux through the membrane. Due to the electro-osmotic flow in the membrane having the same order of magnitude as the filtration rate, it was found that no correction of the filtration rate with the electro-osmotic flux would lead to underdetermined values of the average specific cake filtration resistance. The effect of electrolyte concentration on the cake characteristics was also analyzed theoretically and experimentally.

Keywords:

• Crossflow microfiltration
• Electric field
• Electrophoresis
• Electroosmosis

Acknowledgment

The authors would like to express their gratitude to the National Science Council of ROC, for financial support.