Identification of Fouling Mechanism During Ultrafiltration of Stevia Extract

Stevioside is one of the naturally occurring sweetener, which can be widely applied in food, drinks, medicine, and daily chemicals. Membrane separation has potential application in clarification of stevioside from pretreated stevia extract by ultrafiltration. In the present study, namely 5-, 10-, 30-, and 100-kDa molecular weight cutoff membranes have been used. Quantification of membrane fouling during ultrafiltration is essential for improving the efficiency of such filtration systems. A systematic analysis was carried out to identify the prevailing mechanism of membrane fouling using a batch unstirred filtration cell. It was observed that the flux decline phenomenon was governed by cake filtration in almost all the membranes. For 100 kDa membrane, both internal pore blocking and cake filtration are equally important. Resistance in series analysis shows that the cake resistance is several orders of magnitude higher than the membrane resistance. The cake resistance is almost independent of transmembrane pressure drop, which indicates the incompressible nature of the cake. A response surface analysis was carried out to quantify the development of cake resistance with time during ultrafiltration of various membranes. Quality parameters show that the 30-kDa membrane is better suited for clarification purposes. Identification of the fouling mechanism would aid in the process of design and scaling up of such clarification setup in future.