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PĂ©rez-Correa (2004)

17.2.4 Oxygen Consumption and Carbon Dioxide Production

O2 consumption and CO2 evolution are of particular interest, since they represent the most convenient way of on-line monitoring of the growth in a bioreactor. Furthermore, in aerobic systems, as mentioned in Sect. 17.2.1, the heat generation rate is typically directly proportional to the O2 consumption rate. It is therefore of great interest to model either or both of O2 consumption and CO2 production within the bioreactor model.

The expression for O2 consumption within an O2 balance equation will be:

1 dX

yxo dt where rO, also called the oxygen uptake rate (OUR), is the overall rate of O2 consumption (mol-O2 h-1), YXO is the yield of biomass from O2 (kg-dry-biomass mol-O2-1), and mo is the maintenance coefficient for O2 (mol-O2 kg-dry-biomass-1 h-1).

The expression for CO2 evolution within a CO2 balance equation will be:

dt where rC, also called the carbon dioxide evolution rate (CER), is the overall rate of CO2 production (mol-CO2 h-1), YCX is the yield of CO2 from biomass (mol-CO2 kg-dry-biomass-1), and mc is the maintenance coefficient for CO2 (mol-CO2 kg-dry-biomass-1 h-1).

Typical values of the gas metabolism parameters that have been reported in the literature are shown in Table 17.4. The following subsections outline a procedure by which they may be determined experimentally during the initial studies of growth kinetics. It is necessary to do these experiments in a system in which both the O2 consumption and the biomass can be measured, such as "membrane filter culture" (Sect. 15.3.1). The procedure is based on the case in which the O2 uptake rate is measured, but exactly the same steps can be taken if measurements are done with the CO2 evolution rate.

Table 17.4. A selection of reported gas metabolism yield and maintenance coefficients Sym- Organism Value Reference

bol

YCX

Rhizopus oligosporus

0.76394 kg-CO2 kg-X-1

Sargantanis et al. (1993)

mc

Rhizopus oligosporus

0.031 kg-CO2 kg-X-1 h-1

Sargantanis et al. (1993)

YXC

Gibberella fujikuroi

1.0496 kg-X kg-CO2-1

Thibault et al. (2000b)

mc

Gibberella fujikuroi

0.0150 kg-CO2 kg-X-1 h-1

Thibault et al. (2000b)

mo

Gibberella fujikuroi

0.0130 kg-O2 kg-X-1 h-1

Pajan et al. (1997)

mc

Gibberella fujikuroi

0.0140 kg-CO2 kg-X-1 h-1

Pajan et al. (1997)

YXO

Gibberella fujikuroi

0.9510 kg-X kg-O2-1

Pajan et al. (1997)

YXC

Gibberella fujikuroi

0.625 kg-X kg-CO2-1

Pajan et al. (1997)

mc

Gibberella fujikuroi

0.12 kg-CO2 kg-X-1 h-1

Perez-Correa and

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