Page 436 - Elements of Chemical Reaction Engineering Ebook

Sec. 7.5 Bioreactors 407

Figure 7- 17 shows production rate, cell concentration, and substrate concentra-
tion as functions of dilution rate. We observe a maximum in the production
rate and this maximum can be found by differentiating production with respect
to the dilution rate D:

--
d(DCc) - ()
dD

Maximum rate of
cell production
(DC,)

I
Drnaxprod D
Figure 7-17 Cell concentration and production rate as a function of dilution rate.

Then

Maximum rate of (7- 136)
cell production

7.5.8 Oxygen-Limited Fermentation

Oxygen IS necessary for all aerobic fermentations (by definition). Main-
qning the appropriate concentration of dissolved oxygen in fermentation is
idportant for efficient operation of a fermentor. For oxygen-limited systems, it
is necessary to design a fermentor to maximize the oxygen transfer between
the injected air bubble and the cell. Typically, a fermentor contains a gas
sparger, heat transfer surfaces, and an impeller, for a batch reactor. A clhemo-
stat has a similar configuration with the addition of inlet and outlet streams.
The CD-ROM discusses the transport steps from the bulk liquid to and .within
the nzicroorganism. A series of mass transfer correlations area also given.

7.5.9 Scale-up

Scale-up for the growth of microorganisms is usually based on maintain-
ing 8 constant dissolved oxygen concentration in the liquid (broth), indepen-