Operating a Chemostat (CSTR Bioreactor)

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.

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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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