Continuous Cultivation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 660

12.27. A CSTR is being operated at steady state. The cell growth follows the Monod growth
law without inhibition. The exiting substrate and cell concentrations are measured as
a function of the dilution rate, and the results are shown in Table P12.27 . Of course,
measurements are not taken until steady state is achieved after each change in the flow
rate. Neglect substrate consumption for maintenance and the death rate and assume
that YF P/S is zero. For run 4, the entering substrate concentration was 50 g/L and the
volumetric flow rate of the substrate was 2 L/s.

TABLE P12.27

D, s L 1 Run S , g/L X , g/L

1 1 1 0.9

2 3 1.5 0.7

3 4 1.6 0.6

4 10 1.8 4

(a) Determine the Monod growth parameters: m max and K S .

(b) Estimate the yield factor, YF X/S and YF S/X .
12.28. The growth of bacterium Stepinpoopi can be described by the logistic growth law

1 X
X N

m G ¼ m max

0.5 h 1 and the carrying capacity

with the maximum specific growth rate m max ¼

X 20 g/L. The substrate is in excess.

(a) The cell growth is to be carried out in a 2-L batch reactor. Plot the growth rate and
cell concentration (g/L) as functions of time after inoculation of 0.4 g of cells into
the reactor (ignore the lag phase).
(b) The batch vessel in part (a) is to be turned into a chemostat. Derive an equation for
the washout rate. Plot the cell concentration as a function of dilution rate.

N ¼

Q , S 0

X , S Q

S e ,

Waste water

Effluent

Separator

(1 + R ) Q X e

V, X, S

RQ
S R =

Air

RQ
S R ,

S

X R

X R = c R X e

Activated sludge reactor

FIGURE P12.26 A schematic of waste treatment system.