| dc.description.abstract | The objectives of this study included: (1) Through the theoretical analysis of Hermia modified model to understand the parameters that affect the trend of flux curve for ultrafiltration (UF) membrane process; (2) Carried on the experiments to understand the effects of various particle sizes (62, 99, 130 and 280nm) and concentrations (50, 100 and 200mg/L) in water as well as different operating pressure (2, 3 and 4kg/cm2) and cross-flow velocity (0.01, 0.03 and 0.05m/s) on the performance of UF process; and (3) By means of simulation and verification of Hermia modified model to understand the fouling mechanisms on UF process.
The results of theoretical analysis show that the initial decline velocity of flux in per unit time (-dJ/dt) was affected significantly by the constants of the fouling modes. In general, -dJ/dt is increased linearly with the increase of the model constant that could be the indicator of the extent of fouling.
The experimental results indicated that -dJ/dt was increased with the decrease of particle size and the increase of particle concentration in water. This means reducing the particles size and increasing the particle concentration of feed water would accelerate the trend of membrane blocking, which resulted in lower flux at the later period of filtration. In addition, the increase of operating pressure also increase -dJ/dt, but the variation of cross-flow velocity in the range of this study had no significant effect on -dJ/dt. However, higher flux was obtained with the increase of operating pressure and cross-flow velocity at the later period of filtration. The SEM observation of membrane surface at the end of filtration revealed that increasing cross-flow velocity could reduce the cake thickness formed on the membrane surface.
Simulation of Hermia modified model based on the flux data of experimental results, it found that the flux curve could be fitted very well by intermediate blocking model for the initial fast flux decline stage and by cake filtration model for the slow change of flux at the steady stage of filtration. Consequently, using intermediate blocking model and cake filtration model to simulate the overall variation of flux by two-stage is more suitable (R-square is greater than 0.99) to explain the fouling mechanism of UF membrane filtration.
The results of experimental simulation and theoretical analysis revealed that there was no standard blocking mechanism occurred in this study because the particle size used in this experiment were all larger than the membrane pore size. In addition, the change tendency of simulated constants of intermediate blocking model (Ki) was consistent with the variation of the initial flux decline velocities (-dJ/dt). Therefore, it could be predicted that the intermediate blocking mechanism is suitable to explain the fouling phenomenon in the preceding period of filtration. On the other hand, the constants of cake filtration model (Kca) had insignificant relationship with the variation of flux in the preceding period of filtration, thus the cake filtration mechanism is inadequate to explain the fouling mechanism for the beginning of UF filtration.
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