production of the active substance that is sought after. On the other hand, more and more
complex biotransformations are taking place within bioreactors. Some of them involve
different phases, namely in biocatalysis in organic media, and the interplaying reactions
are sometimes difficult to explain with the conventional models.
The same applies to gas-solid, liquid-solid or solid-solid transformations where in
several instances it will be the structure of one of the phases, or its distribution inside the
bioreactor that is going to control the final product yield.
Recently bioreactors were proposed for large-scale production of complex metazoan
organisms. New problems arose, especially in those cases where sexual reproduction is
compulsory. The problems will be still more complex whenever sexes exhibit different
morphologies or physical properties. Another level of complexity will then be brought
about, because the consideration of extra solid phases will be unavoidable.
All the aforementioned cases deal with multiphase bioreactors. In most of them, the
quest for homogeneity is no longer a matter of concern. On the contrary, the absence of
homogeneity is the rule. The number of liquid or solid phases may be greater than one,
and, in several cases—membrane bioreactors, high-density cell cultures, fixed-film
bioreactors, among others—phase segregation is a must, in order to optimise products
recovery. We are thus obliged to consider the appropriate design of a multiphase
bioreactor, each of which may be a special case with totally new questions to solve.
Research on this field will need new methodologies, able to deal with the different
phases interplaying within the same time window. Eventually, new mathematical tools
will be necessary, as well as new experimental methodologies.
That is why the present work was divided into three different parts. Part I presents new
methodologies that are being successfully applied to the study of multiphase bioreactors.
Part II is devoted to the presentation of bioreactors that, by their very own design, are
specially fitted to deal with multiphase bioprocesses, and which may, in some instances,
be the first solution for a multiphase reaction. Part III is devoted to the presentation of
several case studies, where different approaches were used to solve real multiphase
reaction problems.
We are convinced that, in the forthcoming years, a very active and flourishing area
will emerge, dealing with these special kinds of bioreactors. We expect that this work
will be helpful to all those who are at present struggling to increase the productivity of a
bioprocess where multiple phases are playing a central role.
Joaquim Cabral
Manuel Mota
Johannes Tramper
avery
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