Rheology of Bioprocess Fluids…

…with particular reference to fermentation broths.

References

Doran, Chapter 7

Blanch and Clark, Chapter 5

Atkinson and Mavituna, Chapter 11

Olsvik, E. and Kristiansen, B., "Rheology of Filamentous Fermentations",

Biotechnol. Adv., 12, 1-39 (1994).

Inter-relations between viscosity and broth processing

Rheology of Fermentation Fluids

Bioreactor performance influenced by broth rheology, which is determined by:

biomass concentration

morphology

biomass growth rate

extracellular components

As these parameters typically very throughout the course of a fermentation, so too

will the rheology.

correlations which describe viscosity as a function of biomass concentration only

are of limited value

Medium

ProductFormation

CellMorphology

Cell Growth

Viscosity

BioreactorConditions

Broth HandlingDSP

MixingRequirments

MassTransfer

HeatTransfer

polymer solutions, paper pulp suspensions often used to simulate flow behaviour

of fermentation broths, but they do not include effects of active biomass on system

performance

Correlations for broth viscosity

Vand equation for a suspension of spheres (volume fraction ) in a Newtonian liquid

of viscosity L:

Limited applicability; valid for yeast/spore suspensions < 14 vol% solids.

dependency of on biomass generally stronger than predicted by Vand Equation

Correlations for mycelial systems based on biomass concentration

Authors Correlation

Takahashi and Yamada (1960) 1.1

Deindorfer and Gaden (1955) y 2.3-2.5

Solomons and Weston (1961) 2.65

(cell dry weight conc.), (shear stress), y (yield stress)

Correlations for Power-Law Broths

System Correlation

A. niger k 3.3

P. chrysogenum k 2.5

S. levoris k 0.7

(Allen and Robinson, 1990)

but

Rheological parameters (k, n, y ) also influenced by specific growth rate, DO,

osmotic pressure of medium. (Olsvik and Kristiansen)

Insert pages!

Influence of System Morphology

e.g. Penicillium, Aspergillus, Streptomyces broths

Casson Plastic Model

(metz et al., 1979)

Kp Lhgu0.6

y Le0.8 2.5

Where Le is the hyphal length, Lghu is the hyphal growth unit (total hyphal length/no.

of tips)

Correlation found to be applicable for batch experiments, but not for continuous

(possibly due to differences in cell flexibility)

Power law Model

Fatile (1985)

K 0.3 dp0.2

n -0.06 dp-0.08

Where is the biomass concentration (dry weight) and dp is the aggregate diameter

Frequently, as , K , n , but no simple relationship exists between solids

concentration and rheology.