Guide for Bioreactor Selection

The answers to the questions and issues raised in Sect. 3.2 will determine which of the bioreactor types shown in Fig. 3.2 is most suitable. Figure 3.3 shows how the various considerations might be used to arrive at the decision to use a particular bioreactor. For example, if the microorganism is very sensitive to shear, then a bioreactor type with a static bed must be chosen. This might cause heat removal to be a problem. If some shear can be tolerated, it is not clear which of the agitated bioreactors is best, since shear effects during the mixing of solids in the various bioreactors are not well understood.

Figure 3.3 can give only general guidelines about bioreactor choice. The final decision comes down to bioreactor performance for a particular substrate-microorganism-product combination. However, it is not a simple matter, on the basis of laboratory-scale studies, to say which bioreactor design will perform best at large scale. Also, typically, neither large-scale nor even pilot-scale bioreactors of the various types will be available for comparative studies. Nor is the budget for the development process likely to be sufficient to build several pilot-scale bio-reactors. One of the main arguments of this book is that, in the face of these limitations, mathematical modeling of bioreactor performance is a very useful tool in such scale-up tasks. Scale-up should not be done solely on the basis of experimental studies; rather it should involve a combined experimental and modeling program. This issue will be returned to in Chap. 5, after a consideration of basic heat and mass transfer principles in Chap. 4.

Does the process involve batches of only a few kilograms?

no yes

Use other bioreactor types

Does the organism tolerate frequent or continuous mixing?

not very well

Mixing should be minimized. Use static or infrequently-mixed beds

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