Bioreactor Design and Operation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 958

where C is the concentration of total available adhesion sites on surfaces in the reactor and

s

K

X is the surface adhesion coefficient.
Surface adhesion delays washout in a chemostat. The cells adhered on the vessel
surfaces are less likely to be taken out of the reactor by the outflowing stream. However,
the adhesion e desorption balance eventually leads to the washout if the flow rate exceeds
the critical limit. The washout is more gradual if cells adhere to the vessel surfaces, and
a log tail could exist if the adhesion is strong.

s

Further Reading

Aiba, S., Humphrey, A.E., Mills, N.F., 1973. Biochemical Engineering. 2nd ed. Academic Press, New York.
Bailey, J.E., Ollis, D.F., 1986. Biochemical Engineering Fundamentals, 2nd ed. McGraw-Hill Book Co., New York.
Blanch, H.W., Clark, D.S., 1966. Biochemical Engineering. Marcel Dekker. Inc. New York.
Butt, J.B., 1999. Reaction Kinetics and Reactor Design, 2nd ed. Marcel Dekker, Inc., New York.
Doran, P.M., 1995. Bioprocess Engineering Principles, Academic Press. San Diego.
Prave, P., and others. 1987. Fundamentals of Biotechnology, VCH Verlagsgesellschaft, Weinheim, Germany.
Shuler, M.L., Kargi, F., 2006 Bioprocess Engineering Basic Concepts, 2nd ed. Prentice Hall.
Stephanopoulose, G. (Ed.), 1993. Bioprocessing (vol. 3 of Biotechnology. 2nd ed. H.-J. Rehm and G. Reed. (Eds).), VCH,
New York.
Williams, J.A., 2002. “Keys to bioreactor selections.” Chemical Engineering Progress, 98(3), 34 e 41.

PROBLEMS

18.1. The k L a of a small bubble column has been measured as 20 h 1 at an airflow of 4 L/min.
If the rate of oxygen uptake by a culture of Catharathus roseus is 0.2 mmol-O 2 /(g-cell h),
and if the critical oxygen concentration must be above 10% of saturation (about 8 mg/L)
for this plant cell culture, what is the maximum concentration of cells that can be
maintained in this reactor?
18.2. Avalue of k L a 30 h 1 has been determined for a fermentor at its maximum practical

agitator rotational speed and with air being sparged at 0.5 L-gas/(L-reactor
volume $ min). Escherichia coli with a

¼

m O 2 of 10 mmol-O 2 /(g-X h) is to be cultured. The
critical DO concentration is 0.2 mg/L. The solubility of oxygen from air in the
fermentation broth is 7.3 mg/L at 30 C.
(a) What maximum concentration of E. coli can be sustained in this fermentor under
aerobic conditions?
(b) What concentration could be maintained if pure oxygen was used to sparge the
reactor?
18.3. A continuous culture system is being constructed. The fermentation tank is to be
50,000 L in size and the residence time is to be 2 h. A continuous sterilizer is to be used.
The unsterilized medium contains 10 4 spores/L. The value of k d has been determined
to be 1 min 1 at 121 C and 61 min 1 at 140 C. For each temperature (121 C and
140 C), determine the required residence time in the holding section so as to ensure
that 99% of the time 4 weeks of continuous operation can be obtained without
contamination (due to contaminants in the liquid medium).