Abstract
The influence of the zeta-potentials ( ζ-potentials) of membranes and particles in the micro/ultra-filtration of yeast suspensions is investigated. Cylindrical ceramic micro-filtration (MF) and ultra-filtration (UF) membranes were used in this study; alumina and zirconia membranes being used for MF and UF, respectively. The ζ-potentials of particles and membranes were determined and the results used to select the test conditions for the filtration experiments. Choice of appropriate test conditions allows assessment of the importance of changed electrokinetic properties of the membranes and particles in the filtration process. The electrokinetic properties of membranes and particles were altered by changing the pH and electrolyte concentration. The ζ-potentials of ceramic membranes depend on the pH, the ionic strength of the electrolyte seems of lesser importance. The ζ-potential of yeast particles seems to depend on the concentration of electrolyte aluminium sulphate (Al 2(SO 4) 3) and to a much lesser extent on pH. Changes in the size distribution of suspensions of yeast particles suggest that they are flocculated in the presence of Al 2(SO 4) 3. In MF, the best permeate flux is found when Al 2(SO 4) 3 is used and this seems independent of pH. In contrast, in UF the control of pH is the significant factor and the aluminium concentration has a lesser effect. Generally, the best permeate fluxes are found when the yeast is flocculated. The interactions between particles and membranes are important in filtration and the choice of membrane material can influence the optimal conditions for use. Thus, electrokinetic measurements can play an important role in membrane characterisation.
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