Chemical oxygen demand reduction in a whey fermentation

  • Mauro Moresi
  • Alberto Colicchio
  • Fabio Sansovini
  • Enzo Sebastiani
Biotechnology

Summary

The efficiency of Chemical Oxygen Demand (COD) reduction η in the fermentation of whey by Kluyveromyces fragilis IMAT 1872 was studied at various temperatures, lactose concentrations, air dilution ratios and stirring speeds. Their effects on the biomass yield (y) has been determined previously (Moresi et al. in press).

Two different optimal sets of these variables were found according to whether the objective was the production of cell mass or the reduction of COD. The two sets were then compared to establish a strategy for the industrial development of this fermentation process.

The experimental efficiencies of COD removal were submitted to analysis in a composite design. Only the first two principal axes (i.e., the ‘oxygen transfer coefficient’ factor and the ‘stripping’ factor) of canonical analysis were found to be significant by an F-test. Therefore, the observations were fitted with a quadratic expression by using only these factors: the mean standard error was less than 6%.

The yield of cells, expressed as g of dried cells/g of COD removed, varied in this fermentation, but this parameter may be particularly useful for analyzing and optimizing any fermentation process when the culture medium is a mixture of carbohydrates or the main substrate is fully utilized during the initial stages of fermentation.

Nomenclature

A

Air dilution ratio, litre/min of air per litre of liquid, vvm

bij

Generic coefficient of Eq. (2)

Bii

Generic eigenvalue of the matrix of coefficients bij

COD

Chemical oxygen demand, g/l

L

Initial lactose concentration, g/l

N

stirrer speed, min−1

pij

Direction cosine of xj and Vi

s2

variance of regression

T

Temperature, °C

Vi

Generic eigenvector of the matrix of coefficients bij

x1

Dimensionless temperature

x2

Dimensionless lactose concentration

x3

Dimensionless air dilution ratio

x4

Dimensionless stirrer speed

y

Biomass yield, g of dried cells/g of initial lactose

YG

Overall yield for cell growth, g of dried cells/g of COD removed

Greek letters

Δc}

Net biomass accumulation, g/l

ΔCOD

COD reduction per unit volume of liquid, g/l

η

Efficiency of COD reduction, (CODo-CODf)/CODo, dimensionless

ηM

Maximum efficiency of COD reduction, dimensionless

Φ

Degrees of freedom

σ2

Error variance of factorial design

Subscripts

f

Final

o

Initial

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References

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Copyright information

© Springer-Verlag 1980

Authors and Affiliations

  • Mauro Moresi
    • 1
  • Alberto Colicchio
    • 1
  • Fabio Sansovini
    • 1
  • Enzo Sebastiani
    • 1
  1. 1.Instituto di Chimica Applicata e Industriale, Facolta' di IngegneriaUniversita' di RomaRomeItaly

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