Analysis of flux decline using sequential fouling mechanisms during concentration of Syzygium cumini (L.) leaf extract

Experimental studies were performed in a stirred cell for concentration of MF-pretreated extracts from jamun (Syzygium cumini L.) leaves using nanofiltration over a wide range of operating conditions. Performance of nanofiltration process was evaluated in terms of permeate flux, flux decline and extract quality (total polyphenol content, total flavonoid content and antioxidant activity). A total of ten phenolic compounds including six phenolic acids and four flavonoids were identified and quantified in jamun leaf extract using HPLC. A combined sequential model consisting of Hermia's complete pore blocking and cake layer formation based on resistance-in-series theory was considered to explain the flux decline behavior with time. The model calculations were shown to be in excellent agreement with experimental flux data (R2 > 0.90; SD < 2.5%). Experimental results showed that the operating conditions had significant effect on the onset of cake layer formation. The pore blocking resistance was found to be comparable with membrane resistance, while cake layer resistance was 20-40% of membrane resistance. In addition, the permeate flux for MF-pretreated extract was always higher than that for the untreated extract. The present study with the estimated model parameters provided important understandings into the underlying mechanisms of membrane fouling phenomena during concentration of jamun leaf extract.