Effect of Turbidity and Membrane Pore Size on Cross-flow Microfiltration of Apple Cider
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Microfiltration (MF) is a membrane separation process but its main limitation is membrane fouling. In case of apple cider MF, suspended solids (plant cell wall materials, proteins, and polyphenols) are the main contributors to fouling. In this study, the effect of turbidity, an indicator suspended solids quantity, and the membrane pore size on the flux in MF of apple cider was investigated. Raw apple cider experiments ran in a pilot-plant scale MF unit equipped with ceramic membranes of 1.4μm, 0.8μm, and 0.45μm pore sizes, varying turbidity levels, at 6C, 5m/s crossflow velocity and 159 kPa transmembrane pressure. The permeate flux measured MF efficiency; physical-chemical properties of the cider and microfiltered juice evaluated product quality. Significant changes in pH, Brix and viscosity were observed only for cider microfiltered with 0.45μm. At high turbidity, the 1.4μm and 0.8μm membranes resulted in similar permeate final flux (65L/m2h), relative flux decline of 72%; while 0.45μm had the lowest final flux (37L/m2h), relative flux decline of 55%. At low turbidity, 1.4μm, 0.8μm, and 0.45μm resulted in comparable final fluxes (49, 52, 53L/m2h, respectively) and relative flux decline of 61%, 64%, 55%, respectively. The smallest pore size resulted in the highest rejection of particles and lowest flux, but the lowest flux decline; while the largest pore size had a higher flux, but more pronounced flux decay. This suggests that the fouling layer differs at different pore sizes. Thus, membrane pore size and pre-filtration are critical for MF efficiency and can optimize this process for commercial applications.
dissertation or thesis