The influence of membrane charge and porosity upon fouling and cleaning during the ultrafiltration of orange juice

Abstract

The ultrafiltration of orange juice has been performed to separate phytosterols from proteins. Commercial regenerated cellulose acetate (RCA) ultrafiltration membranes of different molecular weight cut offs (MWCOs) of 10 kDa, 30 kDa and 100 kDa were fouled with orange juice and cleaned with Ultrasil 11 over two operational cycles. Fouling and cleaning mechanisms were investigated by using surface zeta potential, Brunauer-Emmet-Teller (BET) analysis and Fourier transform infrared (FTIR) analysis. The RCA conditioned membranes displayed zeta potential values of −0.2 to −31.5 mV. Fouling caused RCA membranes to have a greater magnitude of negative surface charge and cleaning restored the membrane surface charges close to its pristine state. Fouling increased both the total surface area and the total pore volume of all membranes. The total surface area and total pore volume for RCA 100 kDa after fouling increased by 102% and 185%, respectively. Pore area and volume distributions revealed that the porosities were returned close to the original level after cleaning. The recovery flux ratios of RCA 10, RCA 30 and RCA 100 decreased after fouling by 27%, 6% and 10% respectively; and changes were 25%, 9% and 1% respectively after cleaning. The charge of membrane surfaces after two operational cycles and the IR intensity of RCA membrane deposits, varied with MWCO such that RCA 30 > RCA 100 > RCA 10. Ultrafiltration using RCA 10 kDa membrane displayed the best separation efficiency, with 32 ± 4% rejection of phytosterols. and 96 ± 1% rejection of proteins. Changes in membrane surface charge and porosity have been found to affect the RCA membrane performance due to fouling and cleaning during the isolation of phytosterols from orange juice.