Ultrafiltration
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, nanofiltration or gas separation, except in terms of the size of the molecules it retains. Ultrafiltration is applied in cross-flow or dead-end mode and separation in ultrafiltration undergoes concentration polarization.
Process
Ultrafiltration systems eliminate the need for clarifiers and multimedia filters for waste streams to meet critical discharge criteria or to be further processed by wastewater recovery systems for water recovery. Efficient ultrafiltration systems utilize membranes which can be submerged, back-flushable, air scoured, spiral wound UF/MF membrane that offers superior performance for the clarification of wastewater and process water.
Membrane geometries
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 unit area 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
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
Downstream processing (e.g., concentration) of biotechnology-derived proteins (e.g., therapeutic antibodies)
Desalting and solvent-exchange of proteins (via diafiltration)
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
The most prominent UF membrane suppliers are:
Compiled by Rami E. Kremesti M.Sc.