Membrane clarification of pomegranate and carrot juices using scraped surface membrane unit, a comparative study

Abstract

The membrane processes are used for clarification of fruit juices, but fouling is a limiting phenomenon. The blade rotation in scraped surface membrane unit can increase flow turbulence and thus reduce fouling phenomenon. This unit was used to clarify the carrot juice (which has a cloudy texture) and pomegranate juice (which has a non-cloudy texture) to compare the effect of juice texture on the efficiency of process. The process was performed at three transmembrane pressures (1, 1.5 and 2 bar), three feed flow rates (5, 10 and 15 ml/s) and three blade rotation speeds (0, 147.5 and 222.5 RPM) and changes in permeate flux and volume concentration factor (VCF) and fouling mechanism were studied. The results showed that the rotation of the blade, especially at 222.5 RPM, increased the permeate flux and VCF during clarification of both juices. Also, reduction of feed flow rate increases the effectiveness of blade rotation during membrane clarification of juices. Comparison between two juices showed that the increase in permeate flux and VCF after blade rotation for pomegranate juice was higher than the increase value for carrot juice, especially in the early stages of the process. But, decreasing the transmembrane pressure makes the effect of blade rotation on carrot juice that has a cloudy texture more than pomegranate juice that has a non-cloudy texture, especially when the blade rotation speed is low. The cake formation is the main fouling mechanism in the most tests and SEM images confirm that blade rotation has a significant effect on reduction of cake layer thickness.