| Popis: |
Microfiltration and ultrafiltration are increasingly applied in water and wastewater treatment, particularly using inorganic membranes the chemical and mechanical resistance of which are well adapted to most effluents. However, the transport of water through such membranes has not yet been satisfactorily quantified since the water quality is not being easily standardized, e.g. with respect to its concentration in particles, salts and gas. Carbosep and Membralox membranes, having a mean pore diameter in the range of 0.023 to 0.8 μm, were tested with a standard water obtained by prefiltration, reverse osmosis and demineralization. At given filtration conditions, the permeation rate was steady for the less permeable membranes and transient for the membranes having a mean pore diameter higher than 0.05 μm. Permeation velocity was rendered steady by an additional prefiltration through a 0.2 μm filter. The classical unsteadiness of the flow through microfiltration membranes was then attributed to clogging by microscopic particles. Besides, the existence of transition zones between porous media of drastically different granular size introduces major discrepancies between the predicted and the measured hydraulic resistance. The less permeable membranes are the ones most sensitive to this boundary layer resistance. |
