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The effects of mixing on bioprocesses. Concentration distributions and mechanical shear stress

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Abstract

The effects of mixing on batch alcohol fermentation of diluted solutions of starch hydrolysate is studied. The results of a limited number of samples simultaneously drawn at different locations in the reactor and after different reaction times have been used in a simple mathematical model to provide a picture of the concentration distributions within the reaction environment. The optimal mixing conditions for the fermentation are met at rotation speeds between 1.7 and 5.0 s−1, while the broth homogeneity obviously increases indefinitely with increasing this parameter. This suggests the existence of a shear stress for the biomass, whose effect increases with the application time and seems to affect the process mainly at the end of the fermentation.

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Abbreviations

S kg/m3 :

substrate concentration

P kg/m3 :

product concentration

X kg/m3 :

biomass concentration

t h:

fermentation time

t s h:

application time of shear stress

D h−1 :

dilution rate

μ h−1 :

specific growth rate

k s kg/m3 :

saturation constant of Monod equation

Y x/s :

yield of growth on substrate

Y p/s :

yield of product on substrate

Y x/p :

yield of growth on product

Pg W:

power consumption

N P :

power number

N s−1 :

rotation speed

d kg/m3 :

broth density

D t m:

tank diameter

D i m:

impeller diameter

H L m:

liquid depth

H i m:

location of the impeller from bottom of the vessel

W i m:

impeller width

y m:

distance from bottom of the vessel

x m:

distance from the shaft

max:

maximum value

th:

theoretical value

o:

starting value

A,B,C,D,E:

values referred to different sampling positions

References

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Authors and Affiliations

  1. Institute of Chemical Engineering Science and Technology, University of Genoa, Via Opera Pia 15, 16145, Genoa, Italy

    A. Converti, M. Del Borghi & G. Ferraiolo

  2. IRITECNA, Via di Francia 1, 16126, Genoa, Italy

    C. Sommariva

Authors
  1. A. Converti
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  2. C. Sommariva
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  3. M. Del Borghi
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  4. G. Ferraiolo
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Converti, A., Sommariva, C., Del Borghi, M. et al. The effects of mixing on bioprocesses. Concentration distributions and mechanical shear stress. Bioprocess Engineering 9, 183–189 (1993). https://doi.org/10.1007/BF00369401

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  • DOI: https://doi.org/10.1007/BF00369401

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