Summary
The biomass yields (y) and COD reduction efficiencies (η) of a whey fermentation by Kluyveromyces fragilis were studied in a 100-1 fermenter at various stirrer speeds and lactose concentrations, and compared to those obtained in 10-1 and 15-1 fermenters at constant values of the oxygen transfer coefficient (kLa) and air velocity.
The empirical models previously constructed by using the 15-1 fermenter data could be used to predict the yields on the other scales by calculating for each run the 15-1 fermenter which would provide the same oxygen transfer coefficient measured by the sulphite method on each fermenter under study.
To make this model independent of stirrer speeds used in each generic fermenter, the effect of aeration and mixing was incorporated into an overall parameter (kLa) and the values of y and η were correlated only with temperature, lactose level and kL a, since these variables were approximately orthogonal.
The validity of this model was finally checked against the yields reported by Wasserman et al. (1961) in a 6-m3 fermenter, thus confirming the capability of the model to provide a reliable basis for further scale-up on the production scale.
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Abbreviations
- A:
-
Empty section of the fermenter, m2
- COD:
-
Chemical oxygen demand, g·l−1
- Fj :
-
Generic principal axis of Eq. (9)
- kLa:
-
Volumetric oxygen transfer coefficient, h−1
- L:
-
Initial lactose concentration, g·l−1
- mij :
-
Direction cosine of xi and Fj
- n:
-
Number of experiments
- N:
-
Stirrer speed, min−1
- N′:
-
Equivalent stirrer speed as defined by Eq. (2), min−1
- OTR:
-
Overall oxygen transfer rate, mol·(1·h)−1
- pij :
-
Direction cosine of xi and Vj
- Q:
-
Air flow rate, 1·min−1
- s:
-
Standard deviation
- 2:
-
Variance
- T:
-
Temperature, °C
- vS :
-
Superficial air velocity, m·h−1
- Vj :
-
Generic principal axis of Eq. (10)
- y:
-
Biomass yield, g of dried cells/g of initial lactose
- x1 :
-
Dimensionless temperature
- x2 :
-
Dimensionless lactose concentration
- x3 :
-
Dimensionless superficial air velocity
- x4 :
-
Dimensionless stirrer speed
- x5 :
-
Dimensionless oxygen transfer coefficient
- xT :
-
Dimensionless temperature as defined in Table 9
- xL :
-
Dimensionless lactose concentration as defined in Table 9
- x0 :
-
Dimensionless oxygen transfer coefficient as defined in Table 9
- α,β,γ:
-
Generic correlation coefficients of Eq. (1)
- η:
-
Efficiency of COD reduction, (COD0-CODf)/COD0, dimensionless
- μ:
-
Mean of the experimental values of kLa, h−1
- f:
-
Final
- o:
-
Initial
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Blakebrough, N., Moresi, M. Modelling of the process yields of a whey fermentation. European J. Appl. Microbiol. Biotechnol. 13, 1–9 (1981). https://doi.org/10.1007/BF00505333
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DOI: https://doi.org/10.1007/BF00505333