ultrafiltration

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Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane. This separation process is used in industry and research for purifying and concentrating macromolecular (10³ - 10⁶ Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from microfiltration or nanofiltration, except in terms of the size of the molecules it retains. Mostly, ultrafiltration is applied in cross-flow mode and separation in ultrafiltration undergoes concentration polarization.

Membrane Geometries

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Spiral wound module:
Consists of large consecutive layers of membrane and support material rolled up around a tube Maximizes surface area
Less expensive, however, more sensitive to pollution.
Tubular membrane:
The feed solution flows through the membrane core and the permeate is collected in the tubular housing.
Generally used for viscous or bad quality fluids.
System is not very compact and has a high cost per m2 installed
Hollow fiber membrane:
The modules contain several small (0.6 to 2 mm diameter) tubes or fibers.
The feed solution flows through the open cores of the fibers and the permeate is collected in the cartridge area surrounding the fibers.
The filtration can be carried out either “inside-out” or “outside-in”

Ultrafiltration Module Configurations

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Pressurized system or pressure-vessel configuration:
TMP (transmembrane pressure) is generated in the feed by a pump, while the permeate stays at atmospheric pressure.
Pressure-vessels are generally standardized, allowing the design of membrane systems to proceed independently of the characteristics of specific membrane elements.

Immersed system:
Membranes are suspended in basins containing the feed and open to the atmosphere.
Pressure on the influent side is limited to the pressure provided by the feed column.
TMP is generated by a pump that develops suction on the permeate side.
Ultrafiltration, like other filtration methods can be run as a continuous or batch process

Applications

• Dialysis and other blood treatments
• Concentration of milk before making cheese
• Fractionation of proteins
• Clarification of fruit juice
• Recovery of vaccines and antibiotics from fermentation broth
• Laboratory grade water purification
• Wastewater treatment
• Drinking water disinfection (including removal of viruses)
• Removal of endocrines and pesticides combined with Suspended Activated Carbon pretreatment

See also

• Ultrafiltration (industrial)
• Ultrafiltration (renal)
• Aquapheresis

References

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• Rizvi, S. Membrane Separations in Bioprocessing, Food Science Dept. Cornell University

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