Steam sterilization, membrane systems

Zirconia membranes on carbon supports were originally developed by Union Carbide. Ultrafiltration membranes are commercially available now under trade names like Ucarsep and Carbosep. Their outstanding quality is their high chemical resistance which allows steam sterilization and cleaning procedures in the pH range 0-14 at temperatures up to 80°C. These systems consist of a sintered carbon tube with an ultrafiltration layer of a metallic oxide, usually zirconia. Typical tube dimensions are 10 mm (outer diameter) with a wall thickness of 2 mm (Gerster and Veyre 1985). 

Figure 19. Iri situ steam sterilization of the membrane ultrafiltration system.

In selecting a membrane material, its pH compatibility and wettability should be considered. Some hydrophobic membranes require prewetting with a low-surface-tension solvent such as alcohol, whereas cartridges containing membranes are often presterilized using gamma irradiation. Such filter systems do not require assembly and steam sterilization. 

The system mnst be sterilized before filtration starts every morning, as described in the Section on flat-sheet filters (Section 11.7.4). The sterilizing flnid, either steam or hot water at 90°C, is circulated at low pressure in the same direction as filtration. Water mnst be preflltered to avoid damaging the membranes. Once the equipment has been sterilized, it is cooled with filtered cold water. 

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