Bioreactor Design and Operation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 953

1.4

1.2

1.0

0.8

0.6

0.4

Increasing K X

0.2

K X = 100 L/g

K X = 0

K X = 10

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

D , h -1

FIGURE 18.16 Effect of surface adhesion of cells on the continuous culture on the effluent biomass concen-
tration from a chemostat.

Fig. 18.16 shows the effect of wall adhesion on the effluent biomass concentration with
parameters from Fig. 18.15 . One can observe that when no wall adhesion exists, the biomass
concentration rapidly drops to zero as the dilution rate increases near the washout limit. As
the adhesion isotherm constant K

X is increased, the tail elongates or the biomass concen-
tration decreases much slower at higher dilution rates.
Example 18-4. After a batch fermentation, the system is dismantled and approximately
75% of the cell mass is found to be suspended in the liquid phase (1 L), while 25% is
attached to the reactor walls and surfaces of the internals in a thick film of 3 mm. Work
with radioactive tracers shows that 50% of the target product (intracellular) is associated
with each cell fraction. The overall productivity of this lab reactor is 5 g/L. What would
be the overall productivity at 60,000-L scale if both reactors had a height to diameter ratio
of 2.5 to 1?
Solution. Both reactors are geometrically similar. We can calculate the diameter and the
resulting surface area from the given reactor volume.
V ¼ 4 D

s

H ¼ 4 D

5 8 D

R R R

2:5D R ¼ (E18-4.1)

8 5p

2
3

1
3

2
3

R

S R ¼ pD R H ¼ 2:5pD ¼ 2:5p ¼ 2ð5pÞ V (E18-4.2)

For the 1-L lab reactor, the productivity is from two sources:

(1) Suspended cells, 5 1 ½g ¼ 2.5 g.

) 1/3 1 2/3 .

(2) Surface attached cells, 2.5 g ¼ X S 2(5 p