138
Chapter 5
Y'™c
= 1.64 C -m ole glucose (C -m ole D W
)'1
mglc
= 0.032 C -m ole glucose (C -m ole D W h
) 1
Y'scu
= 2-69 C -m ole citrate (C -m ole D W
) 1
U sing Eqs. (7) and (
8
) and the experim entally determ ined yield coefficients one obtains:
1.64 = 1.14 +
(0.43 +
) - 0.176P/Q
2P /0 + 0.667
2.69 = 2.01 +
(0.73
+ K X) -
0.917P/Q
1.5P/0 + 4/18
(
8
)
(9)
Solving these tw o equations for
Kx
and P/O one finds values o f 0.708 m oles A T P (C -m ole b io m ass
) 1
(corresponding to 26.8 m oles A T P (g D W )'1) and 0.68, respectively. Furtherm ore, u sin g the estim ated
value for the P /O -ratio together with:
0.032 = ------^
------
2P /0 + 0.667
( 10)
w e find the m aintenance A T P requirem ents to be 2.52 m m oles A T P (g D W )'1. A s a consequence o f the
sim pler m odel applied here these values deviate slightly from those reported by C hristiansen and N ielsen
(
2002
).
T he estim ated P /O -ratio is quite low and this points to a low therm odynam ic efficiency o f the oxidative
phosphorylation (see also Section 4.3). T he consequence o f this is a v ery high oxygen requirem ent o f
B.
clausii,
and this is a serious problem in connection w ith industrial application.____________________________
When metabolic products are formed the above-described models are too simple, but a similar
approach can be applied as illustrated in Example 5.4.
Example 5.4
A erobic grow th o f
Saccharomyces cerevisiae
In Exam ple 3.5 the data o f von M eyenburg w ere analyzed and it w as found that a substantial part o f the
ethanol form ed above
D
cn, had been stripped to the gas phase. W hen the data at
D =
0.30 h
1
is corrected for
the m issing ethanol one obtains the follow ing table o f yield coefficients (all on C -m ole basis).
D
( h 1)
P*
P5o
P„
0.15
0.548
0.452
0.425
0
0.30
0.279
0.366
0.167
0.355
0.40
0.175
0.312
0.044
0.513
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