Conclusions on Group IVa Bioreactors

There are in fact few examples of use at large scale of continuously-mixed, forcefully-aerated bioreactors. Perhaps this is not surprising. The majority of SSF processes involve filamentous fungi, and many of these will not tolerate continuous mixing well. However, there are exceptions: In the work of Nagel et al. (2001a), in which Aspergillus oryzae was cultivated on wheat grains, it appears that the fungus grew underneath the seed coat and was thereby protected from shear forces, although of course this would have meant restricted availability of O2. On the other hand, processes involving bacteria should tolerate mixing well and therefore such processes might be expected to be suitable for the continuous-mixing mode of operation.

There is not yet sufficient knowledge to allow a judgment as to whether mechanical agitation or gas-based agitation (i.e., gas-solid fluidized beds) will be better for the continuously-mixed mode of operation.

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