Industrial Biotransformations

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5 Basics of Bioreaction Engineering
Tab. 5.2 Issues involved in scaling-up [35].
Physical property/unit Considerations during scale-up
1. mixing
1.1 mechanical agitation higher stirring speeds for efficient mixing
change in impeller design/multiple impellers
change in ratio of reactor diameter to height
change in reactor type
top-drive or bottom-drive mixing
1.2 aeration change in sparger design
change in ratio of volumetric air flow rate to cross-sectional area of
reactor
foaming – anti-foam agents or mechanical foam separators
increase in superficial gas velocity for constant aeration rate –
limited by flooding
2. heat transfer efficient removal of heat generated by reaction itself and by broth
agitation
with increase in reactor size, ratio of surface area available for heat
transfer to reactor volume can decrease at constant aspect ratio
vigorous mixing ensures better heat transfer but has its own limitations
lowering temperature of cooling water if viable
external or internal cooling; double-jacket, full pipe or half-pipe cooling
Material of construction
3. power consumption changes in power requirement for mechanical agitation, aeration and
circulation
affected by rheology in bioreactor
4. rheology changes due to increase in biomass concentration
changes due to formation of mycelial networks in cases with filamentous
fungi as biocatalysts
synthesis of extracellular polysaccharides
baffle design and number
changes due to heat transfer rates
5. biotransformation biocatalyst immobilization method
effect of shear stress and concentration gradients
changes in microorganism metabolism
changes in age profiles of microorganism
changes in regulatory phenomena due to changes in extracellular
environment
ease of sterilization
changes in down-stream processing techniques and/or capacities