Operating a Chemostat (CSTR Bioreactor)
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Cells and substrate are fed to a steady-state chemostat (continuous stirred-tank bioreactor) where they react to form more cells. The cell concentration (dashed blue line) in the reactor is plotted versus the dilution rate 
, which is the feed volumetric flow rate divided by the reactor volume. The concentration of unreacted substrate leaving the reactor (solid blue line) is also shown. The cell production rate (
) is the solid green line. Use sliders to change the feed substrate concentration, Monod constant, maximum growth rate and the cell death rate constant. Washout occurs at a high enough dilution rate that the cells are flushed out of the reactor and 
. Note that the scale on the right 
axis (green) changes as parameters change.
Contributed by: Garrison J. Vigil (September 2015)
Additional contributions by: Rachael L. Baumann, John L. Falconer, and Nick Bongiardina
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA
Snapshots
Details
Rates of cell growth 
, cell death 
and substrate consumption 
are:
,
,
,
,
where 
is the specific cell growth rate (1/s), 
and 
are the cell and substrate concentrations (g/L), 
is the specific death rate constant (1/h), 
is the yield coefficient, 
is the maximum specific growth rate (1/s) and 
is the Monod constant (g/L).
The cell and substrate concentrations are found by solving the CSTR mass balances at steady-state:
,
,
solving for and :
,
,
where is the dilution rate (1/h), 
is the feed substrate concentration (g/L) and 
.
Wash-out (
) occurs when the cell concentration is zero:
.
The maximum rate of cell production (
) is where 
is greatest, or:
,
,
where and are in units of 1/h.
The screencast video at [1] explains how to use this Demonstration.
Reference
[1] Operating a Chemostat (Continuous Stirred-Tank Bioreactor) [Video]. (Sep 1, 2016) www.colorado.edu/learncheme/kinetics/OperatingChemostat.xhtml.
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