Biochemical Reactions - A First Look
91
($„), 0.728; biomass (x), 2.36; ethanol
(pe),
8.85; glycerol (pg), 2.39. The
C 02
production is measured by a
photoacustic method. The CO: concentration in the effluent gas (in the head space) is found to be 2.88
vol %. On a flow-meter the total gas flow (30°C, latm) is determined to 0.25 L min'1. vgf is assumed to be
equal to vg.
a.
Use the data to set up a carbon balance. Show that the data are not consistent, and calculate the
yield coefficient of a missing metabolite.
b.
Calculate the degree of reduction of the missing metabolite. In your opinion what is the source of
the error?
Problem 3.5 Production of poly P-hydroxy butyrate (PHB)
van Aalst
et al
. (1997) studied the formation of PHB by the bacterium
Paracoccus pantotrophus
in a
continuous stirred tank reactor operated at steady state. When growing under N-limitation but with an
excess of the carbon source the organism can build up a large carbon storage that can be used to support
active growth when, or if the N-limitation is lifted. This is part of the clean-up cycle in waste water
treatment plants, but PHB has an independent and increasing interest as a biodegradeable polymer - in
competition with particularly poly-lactide. Although PHB is a part of the biomass it can just as well be
regarded as a metabolic product. Its formula is
P -
CH^jOoj per carbon atom. The remainder of the
biomass (the “active” biomass) has the formula
X -
CHu
3
O
0
.
44
N
0.24
per carbon atom. The organism uses
acetic acid, CH
3
COOH as carbon and energy source. It grows aerobically, and some C 0
2
is produced
together with
X
and
P.
a.
The result of two experiments, one with N-limitation and one with C-limitation are given below.
Dilution rate and
effluent concentration
of substrates
(D
h'1,
S\
m g L 1)
Production rates in mg L'lh'‘
D =
0.5
■^hac = 70
5
NH3= 95
D = 0A
3065
1050
75
sHac= 750
$Nm ~ 10.5_______________
1625
260
420
For each of the two experiments determine the yield coefficients in the black box model
CH
2
0(H A c) -
YM
NH
3
- yw0
2
+
YsxX + YipP + YK
C 0
2
+
YiV
H20 = 0
b.
For each of the two experiments calculate thye exit concentrations of
X
and
P
when there is no
X
or
P
in the feed. Also calculate the inlet concentrations of acetic acid and ammonia.
c.
Could any single kinetic expression describe the results of both experiments?
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