Startup and Steady State in a Chemostat

dilution rate 

-1



0.25

culture maximum time (h)

initial biomass concentration kg/



0.1

initial substrate concentration kg/



feed substrate concentration kg/



feed substrate time (h)

feed biomass concentration kg/



0.02

maintenance coefficient (kg/kg h)

plot

chemostat

	X(t)
	S(t)
	P(t)

D X

This Demonstration shows the operation of a chemostat. Starting up as a batch reactor, the concentrations change with time. After this short transient period, the bioreactor settles into a steady state.

The behavior of a chemostat, also called a continuous reactor, can be characterized by the concentration profiles of the reactants and products.

In this Demonstration,

is time,

is the concentration of a reactant consumed (also called the substrate),

is the biomass (or cell) concentration,

is the concentration of a product and

is the dilution rate. The concentration in a perfectly mixed tank is uniform throughout the vessel and is therefore identical to the concentration of the effluent stream.

Details

The characteristics of continuous operation are as follows:

Snapshot 1: steady state; after an initial startup period, there is no variation of concentrations with time

Snapshot 2: constant reaction rates, where

is the biomass reaction rate,

is the reaction rate of the consumed reactant and

is the product reaction rate

Snapshot 3: Washout of the organisms (cells) will occur when the dilution rate

is greater than the specific growth rate

. This corresponds to the complete removal of cells by flow out of the tank. In many references, including[1], the variables

and productivity

are plotted versus the dilution rate

, which characterizes the steady state in a chemostat. See Related Links.

Some suggestions for the user:

Increase

interactively to note effect on washout.

Change the feed substrate concentration

to alter the steady state.

Investigate the influence of maintenance requirements on the steady-state biomass concentration.

Operate initially as a batch reactor with

D=0

, and switch to chemostat operation with

max

is the maximum specific growth rate, and in this case was set up to

0.3

-1

Calculate

, the biomass-substrate yield, making use of the yield graph.

References

[1] I. J. Dunn, E. Heinzle, J. Ingham and J. E. Přenosil, Biological Reaction Engineering: Dynamic Modelling Fundamentals with Simulation Examples, Second Edition, Weinheim, Germany: Wiley-VCH, 2003.

External Links

Operating a Chemostat (CSTR Bioreactor)

Michaelis-Menten Kinetics in a Chemostat

Multiple Steady States in Continuous Culture with Substrate Inhibition

Permanent Citation

R. Ricardo Sánchez

"Startup and Steady State in a Chemostat"
http://demonstrations.wolfram.com/StartupAndSteadyStateInAChemostat/
Wolfram Demonstrations Project
Published: August 4, 2021