model would include, in addition to those phenomena which have been
mentioned above, the following microscale phenomena:
1. Diffusion of acidic and basic products of metabolism
2. Penetration and the role of penetrative hyphae in enzyme release
3. Mechanistic descriptions of the control of enzyme production, including induction and repression of synthesis
4. The effect of substrate structure on diffusion, since most work has been done
with gel model systems, but real systems are likely to be more complex
5. Diffusion of products, especially those which can cause product inhibition,
and for volatile products, exchange with the interparticle spaces
6. Metabolic production of water, diffusion of water within the substrate
particle, exchange of water between the particle and the interparticle spaces,
the effect of solute production and consumption on water activity, and the
binding of water by capillary or absorptive forces
Such models might show how, at different times during a fermentation, and
under different operating conditions, various of these phenomena may be
limiting. However, the increased power of such a model and the benefits this
brings in accuracy and flexibility would need to be weighed against the greater
effort required to set up and solve the equations, the greater effort required to
determine many of the parameters associated with the microscale transport
and kinetic phenomena, and the experimental effort required to validate
predictions of the model.
5
Bioreactor Design and Macroscale Phenomena Occurring in Bioreactors
The bioreactor is the central point of a fermentation process. It is here that the
biotransformation takes place, that a raw material is turned into a desired and
valued product. Optimization of the rate of formation and yield of product
within the bioreactor is a key part of optimizing the production process.
Although the field of bioreactor design for submerged liquid fermentation
systems is well developed, many of the principles cannot be directly translated
to SSF systems. Solid beds and liquid broths are different: solid beds are not as
easy to mix as liquid broths, and due to poor heat transfer properties of solid
substrate beds, heat removal is much more difficult in SSF than it is in SLF.
5.1
General Roles of a Bioreactor
A solid-state fermentation bioreactor must fulfill one or more of the following
functions:
1. Contain the substrate bed
2. Prevent the uncontrolled release of the process organism into the environment
3. Prevent the entry of contaminants into the process
Biochemical Engineering Aspects of Solid State Bioprocessing
97
mentioned above, the following microscale phenomena:
1. Diffusion of acidic and basic products of metabolism
2. Penetration and the role of penetrative hyphae in enzyme release
3. Mechanistic descriptions of the control of enzyme production, including induction and repression of synthesis
4. The effect of substrate structure on diffusion, since most work has been done
with gel model systems, but real systems are likely to be more complex
5. Diffusion of products, especially those which can cause product inhibition,
and for volatile products, exchange with the interparticle spaces
6. Metabolic production of water, diffusion of water within the substrate
particle, exchange of water between the particle and the interparticle spaces,
the effect of solute production and consumption on water activity, and the
binding of water by capillary or absorptive forces
Such models might show how, at different times during a fermentation, and
under different operating conditions, various of these phenomena may be
limiting. However, the increased power of such a model and the benefits this
brings in accuracy and flexibility would need to be weighed against the greater
effort required to set up and solve the equations, the greater effort required to
determine many of the parameters associated with the microscale transport
and kinetic phenomena, and the experimental effort required to validate
predictions of the model.
5
Bioreactor Design and Macroscale Phenomena Occurring in Bioreactors
The bioreactor is the central point of a fermentation process. It is here that the
biotransformation takes place, that a raw material is turned into a desired and
valued product. Optimization of the rate of formation and yield of product
within the bioreactor is a key part of optimizing the production process.
Although the field of bioreactor design for submerged liquid fermentation
systems is well developed, many of the principles cannot be directly translated
to SSF systems. Solid beds and liquid broths are different: solid beds are not as
easy to mix as liquid broths, and due to poor heat transfer properties of solid
substrate beds, heat removal is much more difficult in SSF than it is in SLF.
5.1
General Roles of a Bioreactor
A solid-state fermentation bioreactor must fulfill one or more of the following
functions:
1. Contain the substrate bed
2. Prevent the uncontrolled release of the process organism into the environment
3. Prevent the entry of contaminants into the process
Biochemical Engineering Aspects of Solid State Bioprocessing
97