Modeling and fouling mechanisms for ultrafiltration of Huanggi (Radix astragalus) extracts

A semi-empirical model has been developed in ultrafiltration of huanggi (Radix astragulus) extracts. Three major fouling resistances were quantified with transmembrane pressure (TMP) ranged from 0.4 to 0.8 bar and process time lasted for 120 min. Adsorption grew fast at the initial 15 min and its contribution was more significant at 0.4 bar, nearly 50%. Pore blocking almost kept the same values of 1.28, 1.84, and 2.39 at pressures of 0.4, 0.6, and 0.8 bar, respectively. Cake layer grew linearly at 0.4 bar but it increased rapidly as the TMP arose. With the TMP increased, the contribution of cake layer became more significant, almost 75% at 0.8 bar which was triple of that at 0.4 bar. Prediction of flux decline fitted quite well with the experimental data, all within 5% errors. It demonstrates that adsorption, pore blocking, and cake layer are the main mechanisms for membrane fouling during the process.