I'm going to describe how to use an interactive simulation that is a model of a continuous
stirred tank bioreactor for cell growth.
I'm showing here a snaphsot of the simulation, and we're plotting concentrations, so here's
the cell concentration for conditions that are selected here as a function of dilution
rate.
So the dilution rate is essentially the feed volumetric flow rate divided by the reactor
volume.
It also shows the substrate concentration, what the cell needs to grow.
A couple things to note in this diagram, as the dilution rate, as we flow material in
faster and faster, we reach a point where there's no consumption of substrate, the cell
concentration drops to zero.
This is called washout, and it's indicated here at what dilution rate we have washout.
The other thing that we're plotting here using the y-axis is the dilution rate times the
concentration of the cell leaving.
It's also the concentration of course of cell entering the reactor, and so this is essentially
our production rate, flowrate times the concentration, and notice it has a maximum somewhere and
we calculate that in this simulation, and then we can change the substrate feed concentration.
We can change one of the constants in the kinetic expression for cell growth, and then
this is essentially the other constant, the maximum growth rate, and then we can also
change the cell death rate.
So we'll look at the simulation and see how as we change these various parameters, the
maximum production rate and the washout rate change.
So here we're looking at the interactive simulation and the important thing to notice is that
the scales on the y-axis on the left is the cell concentration, and the substrate concentration,
and on the left is the concentration in the reactor and therefore leaving the reactor,
of cells times the dilution, and the dilution rate is the volumetric flow rate divided by
the volume.
What I'm looking at is how much product am I making per reactor volume, and if I increase
the feed substrate concentration, notice that the scale on the left changes, increases,
and the scale on the right increases.
More fed substrate, then a faster production.
If I increase the Monod constant, this is in the denominator, and notice now the scale
on the right is decreasing, and likewise if I increase, or similarly if I increase the
maximum growth rate, essentially the rate constant is increasing, then of course the
production rate, the dilution rate times the concentration increases.
When the death rate constant increases, notice that now at zero dilution rate, no flow through
the reactor, everything dies, and now we have a maximum in this cell concentration as a
function of dilution rate, but we have a different location, a different dilution rate that corresponds
to the maximum in the rate that we're producing cells, in other words, number of cells coming
out of the reactor per reactor volume.
And the simulation indicates the point where if we have a high enough flowrate, we just
wash everything out of the reactor.
Hopefully by using this simulation, you get a little better understanding of the behavior
of this type of CSTR bioreactor.