SEALS IN FERMENTORS

One of the most stringent requirements in the design of a fermentor is the ability of the fermentor to maintain strict aseptic integrity throughout the fermentation process. Of course this is applicable in monoseptic fermentation involving a single pure culture fermentation. For such requirements, theretically there should be complete isolation or barrier between the fermentor content and the surrounding environment. This would literalloy mean that the fermentor is completely closed by wall or structure to the environment with no openings or holes that expose the content of the fermentor to the environment.

In reality this is difficult to achieve as fermentors need holes or ports that allow important connections for the insertion of impellers, electrodes, inlet gas and outlet gas and even sampling ports. If this is so then the design of the fermentor must reach a compromise where while on one hand it maintains its aseptic integrity and on the other hand it allows port holes for the necessary components to enter or leave the fermentor but by not compromising its aseptic integrity

The solution to this dilemma is by:
1 Providing seals
2 Maintaining the seals continually aseptic

The seal is especially crucial at the stirrer or agitator entrance to the fermentor. The stirrer is the essential component in any fermentor as it is involves in the mixing and homogennization of the contents of the fermentor. Any seal that is used in the agitator system will have to fulfil various requirements such as:

1 It should be able to maintain the state of aseptic integrity of the fermentor while functioning
2 It should be able to withstand the stress of repeated sterilizations of the fermentor such as SIPs
3 It should be able to withstand the various CIP procedures
4 It should be able to sustain the pressure developed within the fermentor
5 If the fermentor is involved in food and pharmaceutical fermentations, it should be built of sanitary materials
6 The seal components will not contaminate the fermentation process
7 It should be able to isolate the contents inside the fermentor from the external environment

In any seal there is usually a need for:
1 Packing structure within the seal
2 Lubricant to smoothen the rotation of the shaft within the seal
3 Steam sterilization of the seal to ensure no contaminations occurring through the seal

There are other seals within the fermentor which is made up of the O - rings that help in the close air tight sealing between two surfaces. We have discussed this section in previous blogs