Multiphase Bioreactor Design

0.48, εo= 0.045; X·vmax = 0.01 mol/s, = 100 mol/m3, and m=100. The dimensionless
concentrations for a two-phase fluidised bed and three-phase fluidised bed are calculated
and given in Table 12.5 for different recycles.
As little substrate is converted, only a small amount of product is made. The
introduction of the organic solvent results in a smaller product concentration in the
medium phase. In optimising a continuous operation, there is lot of freedom, e.g. the
initial substrate concentration, recycle of medium and/or organic solvent. So, whether a
continuous operation is feasible depends on a total cost calculation of the plant.

Table 12.5 Dimensionless substrate and product

concentrations in a continuously operated fluidised

bed

Two-phase fluidised

bed

Three-phase fluidised

bed

Recycle

Substrate Product Substrate Product Product organic

solvent

0.1 0.9993 6.50e-4 0. 9994 6.07e-4 0.72e-4

0.9 0.9994 0.0061 0.9994 0.0019 2.98e-4

0.99 0.9996 0.0396 0.9994 0.005 8.5e-4

CONCLUSIONS

In this chapter we explore different aspects of liquid-liquid-solid three-phase systems.
The benefits of such a system for typical biotransformations have been discussed in
literature. However, the ideal reactor configuration can still be argued. Different reactor
configurations are discussed here, including a simple three-phase fluidised bed, but also
more elaborate options, such as the different possibilities with a loop reactor. It can be
concluded that building and operating a three-phase system is merely a minor extension
of conventional bioreactors.
For a liquid-liquid-solid three-phase fluidised-bed bioreactor conditions have been
established for which this reactor performs better than a conventional two-phase fluidised
bed. Keeping all parameters constant, changing the operation variables, medium flux and
organic solvent flux, the distribution coefficient is determined, at given maximum
substrate conversion rate, for which the three-phase fluidised bed performs equally well.
It appears that a low distribution coefficient (larger than 1 but less than 2) suffices for a
better performance.
So, it can be concluded that a three-phase fluidised bed, or less simple three-phase
bioreactors, are good options for operating specific biotransformations, provided in situ
extraction is needed for such a specific biotransformation.

NOMENCLATURE

Multiphase bioreactor design 378