Concentration of Fat Globules in Milk by an Oscillating Membrane Unit: Experiment Using Model Emulsified Solutions

Abstract

High speed movement of a membrane parallel to its surface will produce a flow similar to cross-flow filtration adjacent to the membrane surface, which can reduce the concentration polarization, resulting in an increase of the permeation flux. For this purpose, a circular flat membrane unit, which is oscillated circumferentially at high speed, has been developed by a membrane company. In the present study, the newly developed oscillating membrane unit was applied to separate fat globules from an artificially prepared emulsion in order to develop a process applicable to a highly concentrated dairy raw solution, which remains almost unprocessed by a conventional membrane system. The permeation flux and the fat globule concentration were examined using two types of membrane made of polyethersulphone and polytetrafluoroethylene. The results were discussed in terms of the effect of oscillation variables such as amplitude, and membrane characteristics such as pore size and membrane material. The effect of membrane oscillation on the effective cut-off size decreased with an increase of amplitude. The permeation flux and the concentration of fat globules in retentate increased with an increase in amplitude. Due to oscillation, the adsorption of fat globules by the membrane surface or pores was decreased, and there was virtually no fouling of the membrane. The permeation flux was stable in the treatment of skim milk and cheese whey. Small fat globules passed through the relatively large pore size of the hydrophobic membrane, demonstrating the potential for separating small fat globules in skim milk or cheese whey by using the oscillating membrane unit.