Design of Fermentation Processes
387
Figure 9.8. Transient in a constant-Z), stirred tank continuous reactor following a change in substrate
feed concentration from
s/ -
4 g L'1. Kinetic parameters as in Example 9.12, and
D ~
0.4 h'1. A: z =
x /
x(, for
Sf=
8
,
6
and 4 g L'1.
B:
substrate concentration, g L"1.
Figure 9.8 A and B shows the transients of
z ~ x / x0
and of
5
for the same set of kinetic
parameters as were used in figure 9.7. D = 0.4 h
' 1
and ^ = 4 g L 1. It is noted that
s
returns to its
initial value
(s0
=
2A
g L l) as is the case whenever
fi
is a function of
s
alone, and
D
is kept
constant during the experiment. In the beginning there is an overshoot in
s
when
sf> s ) .
There is
not enough biomass available to cope with the larger influx of substrate, but eventually
x
increases to its final valuer* =
x0
+
Ysx (s/-s
f ), i.e
The curves on figure 9.8 were simulated using Matlab to solve
-
flCgZ
+ ( / -
1
) exp(-Z>f)
+ 1
_
D _
dt
” //m“
a ~ fK^z
+ ( / -
1
) exp(-Dr) +
1
Z
(9.98)
with z = 1 for / = 0 ; / = S/ /
Sf
and
X0= xnI
sf). D
= 0.4 h '1.
c
Transients caused by pulse addition of substrate.
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