Experiments on clarification of orange juice and fouling resistances by using ceramic microfiltration membrane

The purpose of this work was to study the clarification of orange juice, membrane fouling resistances and cleaning methods by microfiltration. Ceramic membranes with a pore diameter of 0.2 mm were employed. The changes of permeate flux and the efficiency of retention were investigated during the clarification process. It was found that, at temperature 30℃, transmembrane pressure 0.16 MPa and cross-flow velocity 4 m/s, the steady-state permeate flux reached 22.4 L/(m2·h) in the total recirculation experiment, however the permeate flux was only 10.6 L/(m2·h) in the concentration experiment, which corresponded to the volume concentration factor of 12 and the percentage yield of 91.67% for the clarified juice. The turbidity of clarified juice was 0.62 NTU, the percentage of clarification reached as high as 99.93%, and the main nutrition elements of clarified juice change insignificantly. On the basis of the fouling resistance model, the effects of operating parameters on various resistances and the kinetics of membrane fouling were studied in detail. The results indicate that transmembrane pressure affects significantly the reversible polarized layer resistance; the increase of cross-flow velocity decreases various polarized layer resistances, but affects insignificantly the irreversible fouling resistance; the various resistances decrease with increasing temperature; the fouling kinetics can be describe by a pseudo-second-order equation. The cleaning procedures for fouled membranes were investigated. The results show that permeate fluxes are recovered rapidly by using deionized water, the mixed solution containing 1% NaOH and 0.5% NaClO, 0.2% HNO3 solution to clean the membranes in turn.