Analyses of hydrodynamic resistances and operating parameters in the ultrafiltration of grape must

Abstract

Grape must destined to the production of white wine was clarified by cross-flow ultrafiltration (UF), on laboratory scale, by using polysulphone hollow fibre membranes with a molecular weight cut-off of 100 kDa. The effects of transmembrane pressure (Δ P), feed flow rate ( Q f) and temperature ( T) on permeation flux and resistances were studied. Results showed that permeate fluxes decreased with time until a steady-state was established. A maximum steady-state permeate flux was reached at a Δ P of about 100 kPa. Steady-state permeate fluxes increased with temperature in the range 15–39 °C. It was also observed that flux increased by increasing bulk flow rates according to the concentration polarization model. The permeate flux decay was analysed through the resistance-in-series model. Analyses of results showed that the membrane resistance ( R m) was constant, while both cake layer resistance ( R c) and fouling resistance ( R f) increased with Δ P and decreased with Q f. An increasing of temperature determined a significant decreasing of the cake layer resistance in the range 15–23 °C, while the fouling resistance showed a little increase in all the range of the investigated temperatures. Observed rejections of the UF membrane towards total soluble solids (TSS) and total phenolics increased by increasing Δ P in the range 20–130 kPa. A decreasing of the color intensity associated to an increasing of the clarity of the clarified must was observed when the pressure is raised. pH and acidity of the clarified must were not affected by the operating pressure.