The following table lists the principles of ultrafiltration, microfiltration and reverse osmosis process and operational performance to compare.
Process and operation
Similar to the reverse osmosis process, the microfiltration and ultrafiltration processes must also overcome the effects of concentration polarization and membrane pore clogging. In general, ultrafiltration and microfiltration membrane hole clogging problem is very serious, often need high-pressure recoil technology to be recycled.
Therefore, in the design of microfiltration, ultrafiltration process, in addition to the design of the same reverse osmosis process, pay attention to the choice of membrane surface velocity, liquid turbulence, pretreatment and membrane cleaning and other factors, still need special attention to the Rinse to restore the membrane flux.
As the ultrafiltration process membrane flux is much higher than the reverse osmosis process, so the concentration polarization is more obvious, it is easy to form a layer of gel layer in the membrane, then the membrane flux will no longer increase with the pressure increase , This permeability is called the critical permeate flux.
For a certain concentration of a certain solution, the pressure reaches a certain value after the permeability flux reaches a critical value, so the actual operation should be selected near the critical barrier flux near the operation, this time the pressure is generally 0.4-0.6MPa, too high The pressure is not only useless and harmful.
The operation of the ultrafiltration process is generally the wrong flow, that is, the liquid flow and the membrane surface parallel flow, the material flow rate affects the thickness of the membrane boundary layer, improve the membrane surface velocity is conducive to reduce the concentration of polarization effects, improve the filtration flux, which And reverse osmosis process mechanism is similar.
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