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The effects of membrane morphology and operating conditions on the particle fouling in dead-end microfiltration are studied to verify the criteria for membrane selection. Three kinds of membranes, Isopore, Durapore and MF-Millipore membranes, with similar mean pore sizes around 0.45 μm are used for filtering 0.15 μm PMMA particles. The blocking index and resistance coefficient used for membrane blocking models are analyzed during microfiltration. The membrane pore blocking is dominant and the blocking index decreases gradually in the early filtration period. The blocking index drops suddenly to zero when a critical condition reaches; and the filtration follows up the cake filtration model thereafter. A membrane blocking chart is established for relating the blocking index and operating conditions for the used membranes. Comparing the results under a fixed filtration pressures, the blocking occurred in Isopore membrane is the most serious. The use of MF-Millipore membrane causes a filter cake to more easily form on the membrane surface. While the use of Durapore membrane results in the highest filtration flux due to its antifouling behavior. To analyze the critical filtration flux and particle accumulation at the changing point of blocking models, the sequence of difficulty in transforming to cake filtration is Isopore > Durapore > MF-Millipore membrane. The force analysis on depositing particles shows that a power relationship exists between the overall filtration resistance and filtration pressure at the critical condition. The critical overall filtration resistance has a sequence of Isopore > Durapore > MF-Millipore membrane under a fixed filtration pressure. |
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