Continuous Cultivation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 652

PROBLEMS

12.1. Pseudomonas sp . has a mass doubling time of 2.4 h when grown on acetate. The
saturation constant using this substrate is 1.3 g/L (which is unusually high), and cell
yield on acetate is 0.46 g cell/g acetate. If the feed stream to a chemostat contains
38 g/L acetate, determine:
(a) Maximum dilution rate,
(b) Cell concentration when the dilution rate is one-half of the maximum,
(c) Substrate concentration when the dilution rate is 0.8 D max ,
(d) Cell productivity at 0.8 D max
12.2. Consider a 1000-L CSTR in which biomass is being produced with glucose as the
substrate. The microbial system follows a Monod relationship with 0.4 h 1 ,

m max ¼

K S ¼ 0.5 g-biomass/

g-substrate consumed. If normal operation is with a sterile feed containing 10 g/L
glucose at a rate of 100 L/h:
(a) What is the specific biomass production rate (g $ L 1

1.5 g/L (an unusually high value), and the yield factor YF X/S ¼

$ h 1 ) at steady state?
(b) If recycle is used with a recycle stream of 10 L/h and a recycle biomass
concentration five times as large as that in the reactor exit, what would be the new
specific biomass production rate?
(c) Explain any difference between the values found in parts (a) and (b).
12.3. Table P12.3 was obtained in a chemostat for the growth of E. aerogenes on a glycerol-
limited growth medium.
For this system, estimate the values of:
(a) K S , g-glycerol/L
(b) m m $ h 1

(c) YF X/S , g-cells/g-glycerol
(d) m S , g-glycerol/(g-cell $ h)

TABLE P12.3

Glycerol concentration
S

Cell concentration
X Dilution rate D, h L 1 , g/L , g/L

0.05 0.012 3.2

0.10 0.028 3.7

0.20 0.05 4.0

0.40 0.10 4.4

0.60 0.15 4.75

0.70 0.176 4.9

0.80 0.80 4.5

0.84 10.00 0.5

Note: S 0 ¼ 10 g/L.