Dr. Saleha Shamsudin
PPK BIOPROSES, UniMAP
013-2081261
Kinetic of Growth in Continuous Culture
Some specific devices for continuous culture,
derivation for ideal chemostat, application of
chemostat and its deviation of ideality.
Morton Coutts (1904-2004), father of
continuous fermentation
Morton Coutts' plan for continuous fermentation at Dominion Breweries'
Waitemata Brewery was patented as a world first in 1956.
BATCH
Culture environment changes continually
Growth, product formation and substrate utilization
terminate after a certain time interval
CONTINUOUS CULTURE
Fresh medium is continually supplied to a wellstirred culture
Products and cells are simultaneously withdrawn
Growth and product formation can be maintained in
constant environment condition for prolonged
periods in continuous culture and supplies uniformquality products.
Some Specific Devices for Continuous Culture
Chemostat and Turbidostat
Chemostat – constant chemical environment, When
chemostat is at steady state, the nutrient, product and cell
concentrations are constant
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 Ideal Chemostat
The Ideal Chemostat
Fresh
sterile
medium
Cell is
removed at
the same
rate
Control
elements: pH,
DO control units
Volume
(constant)
system is
steady state
Feed media are
sterile,
endogeneous
metabolism or
death rate is
negligible
Cells are removed equal
to their growth rate
which is equal to dilution
rate.
In the chemostat, growth rate is limited by atleast
one substrate, substitute the Monod equation for µg.
A plot of 1/ug versus 1/S can be used to estimate value
for um and Ks. If D<um, we can relate effluent substrate
concentration to dilution rate by:
Material balances on cell and growth-limiting substrate
concentrations around the reactor yield the following:
S0 and S = feed and effluent substrate (g/l)
qp = specific rate of extracellular product formation
Yx/s and Yp/s = yield coefficents
When extracellular product formation is negligible, qp and
the system is at steady state (dS/dt=0)
Eq. 6.70
Since µg=D at steady-state if kd=0
Using eq.
The steady-state cell concentration can be expressed
as;
Consider the effect the inclusion of endogeneous
metabolism; eq. 6.66 becomes:
Substitute Eq. 6.73b into steady-state balance,
assuming no product formation (Eq. 6.70), we find
Equation 6.73 can be rearranged to:
Yx/s
ms = maintanance coefficient; Yx/sAP apparent yield;
Plot 1/ Yx/sAP against 1/D to find ms is the slope and 1/ Yx/sAP
is the intercept
In the present of endogenous metabolism;
Consider the conversion of extracellular substrate
into extracellular product. The balance on product
formation is:
qp is described by equation 6.16, 6.17 and 6.18
depending on the types ofmicrobial products
For substrate balance, Eq. 6.69 becomes:
and yield:
Application of Chemostat
•To grow microorganisms on very toxic nutrients
• To select mutants with a higher affinity to the
growth-limiting nutrient
• To select the species that are optimally adapted to
the growth limitation and culture conditions in a
mixed population
• To study the properties of organisms at selected
growth rates
• To gather steady state data about an organism in
order to generate a mathematical model relating to
its metabolic processes
Continuous industrial microbial processes are
much less common than batch processes, but
most biological waste treatment steps are
operated continuously
I.
Continuous cultivation of rumen
microorganisms, a system with possible
application to the anaerobic degradation of
lignocellulosic waste materials (Huub et al.,
1986)
II. A
bioprocessing mode for simultaneous fungal
biomass protein production and wastewater
treatment using an external air-lift bioreactor
(Bo et al.,2001)
 Continuous
fermentation has been
successfully applied in:
• Brewing industry (Dennis et al., 2000)
• Single cell protein production (King,
1982).