Modeling of continuous cell growth

1. MODELING OF CONTINUOUS
CELL GROWTH
A.SHEIK ABDULLAH(117012101307)
M.SORNAMALYA(117011101309)
M.THASLEEMA PARVEEN(117011101310)
Biochemical engineering06-04-20 1

2. CONTINUOUS CULTIVATION
 The culture environment changes continually in a batch culture.
 Growth, product formation, and substrate utilization terminate after
a certain time interval, whereas, in continuous culture, fresh medium
is continually supplied to well-stirred culture, and products and cell
are simultaneously withdrawn.
 Growth and product formation can be maintained for prolonged
period in continuous culture.
 After a certain period of time, the system usually reaches a steady
state where cell, product, and substrate concentrations remain
constant.
 Continuous culture provides constant environmental conditions for
growth and product formation and supplies uniform-quality product.
06-04-20 Biochemical engineering 2

3. SPECIFIC DEVICES FOR
CONTINUOUS CUTURE
• The primary types of continuous cultivation
devices are the
06-04-20 Biochemical engineering 3
Turbidostat
Chemostat

4. CHEMOSTAT
 The name refers to constant chemical
environment.
 Cellular growth is usually limited by one essential
nutrient, and other nutrients are in excess.
 When a chemostat is at steady state, the nutrient,
product, and cell concentrations are constant.
06-04-20 Biochemical engineering
4

5. 5
Biochemical engineering06-04-20

6. TURBIDOSTAT
 In turbidostat the cell concentration in the culture vessel is
maintained constant by monitoring the optical density of the
culture and controlling the feed flow rate.
 When the turbidity of the medium exceeds the set point, a
pump is activated and fresh medium is added.
 The culture volume is kept constant by removing an equal
amount of culture fluid.
 The turbidostat is less used than the chemostat, since it is
more elaborate than a chemostat because the environment is
dynamic.
 It can be very useful in selecting subpopulation able to
withstand a desired environmental stress because the cell
concentration is maintained constant.
06-04-20 Biochemical engineering
6

7. 7
06-04-20 Biochemical engineering

8. THE IDEAL CHEMOSTAT
 An ideal chemostat is same as a perfectly mixed
contonuous-flow, stirred-tank reactor (CFSTR).
 Most chemostats require some control elements,
such as pH and dissolved oxygen contrl units, to
be useful.
 Fresh sterile medium is fed to the compltely
mixed and aerated reactor, and cell suspension is
removed at the same rate.
 Liquid volume in the reactor is kept constant
06-04-20 Biochemical engineering
8

9. 9
06-04-20 Biochemical engineering

10. A material balance on the cell concentration
around the chemostat yields
FX0 – FX + VRµgX – VRkdX = VR (dX/dt) …1
Where,
F is the flow rate of nutrient solution(1/h)
VR is the culture volume (1)
X is the cell concentration (g/l)
µg & kd are growth and endogenous rate
constants (h-1)
06-04-20 Biochemical engineering
10

11.  If cell mass is the primary parameter, it is
difficult to differentiate cell death from
endogenous metabolism.
 When we use kd we imply that endogenous
metabolism is the primary mechanism for cell
mass decrease.
 With k’d we imply that cell death and lysis are
the primary mechanism of decrease in mass.
 kd could only be a cell death rate
06-04-20 Biochemical engineering
11

12. Eqn 1 rearranged as
(dX/dt) =DX0 + (µg- kd –D)X …..2
Where,
D is the dilution rate and D = F/VR
D is the reciprocal of residence time
X0 =0 (death rate is negligible)
If the system at steady state(dX/dt =0), then
µg = D (if kd =0) …..3
06-04-20 Biochemical engineering
12

13. By substituting Monod’s eqn for µg in eqn 3,
µg = D = (µmS/Ks +S) ……4
Where,
S is the steady state limiting substrate
concentration(g/l)
Eqn 4 is identical to Michaelis-Menten kinetics
We can relate the substrate concentration to
dilution rate for D< µm
S = (Ks D/µm-D) ……5
06-04-20 Biochemical engineering
13

14. A material balance on the limiting substrate in in the
absence of endogenous metabolism yields
FS0-FS-VRµgX(1/YM
(X/S))-VRqpX(1/Y(P/S))=VR(dS/dt)..6
Where,
S0 &S are feed and effluent substrate concentration (g/l)
qp is the specific rate of extracellular product formation (g P/µg cells h)
YM
(X/S) and Y(P/S) are yield coefficients(g cell/g S and g P/g S)
When extracellular product formation is negligible & the system at steady state is
D(S0-S) = (µgX/YM
(X/S)) ……7
µg =D at steady state if kd = 0
X=YM
(X/S)(S0-S) ..….8
X = YM
(X/S)[S0- (KSD/µm-D)] ..9
Consider the effect the inclusion of endogeneous metabolism eqn 3 becomes
D = µg-kd = µnet ....10
µg = D + kd …11
06-04-20 Biochemical engineering
14

15. By substituting eqn 11 into 7
D(S0-S) - (1/YM
(X/S) D+kd)X = 0 …12
D((S0-S)/X) - (1/YM
(X/S) D+kd) = 0 ...13
D(1/YAP
(X/S) )-(D/YM
(X/S) )-(kd/YM
(X/S) ) = 0 ..14
(1/YM
(X/S) )+(kd/YM
(X/S) D)= (1/YAP
(X/S) ) ..15
(1/YAP
(X/S) ) = (1/YM
(X/S) )+(ms/D) ….16
Where, ms = (kd/YM
(X/S) )
Values of (YM
(X/S) ) and ms are obtained from
chemostat experiment by plotting (1/YAP
(X/S) ) and
(1/D). The slope is ms and intercept is (1/YM
(X/S) )
06-04-20 Biochemical engineering
15

16. 16
06-04-20 Biochemical engineering

17. WHY CONTINUOUS CULTIVATION IS
NOT USED IN INDUSTRIES
 Secondary metabolites are produced only
during the stationary phase. Hence the
continuous cultivation is not suitable for them.
 Maintenance of sterility is very difficult.
 High infrastructure cost is required.
17
06-04-20 Biochemical engineering

18. ADVANTAGES
 Works all time: low labor cost, good utilization
of reactor.
 Often efficient: due to the autocatalytic nature
of microbial reactions,
• The productivity can be high.
• Automation may be very appealing.
• Constant product quality.
06-04-20 Biochemical engineering
18

19. DISADVANTAGES
 Promised continuous production for months
fails due to
• Infection
• Spontaneous mutation of microorganism to non
producing strain
06-04-20 Biochemical engineering
19

20. REFERENCES
 Bioprocess engineering basic concepts:
Michael L. Shuler and Fikret Kargi
06-04-20 Biochemical engineering
20

21. 21
06-04-20 Biochemical engineering
THANK
YOU!