What is the difference in the terms of Kinetics between a chemostat (or a continuous flow fermentor) and a fed-batch fermentor with ouflow? Both aim to keep the volume inside the bioreactor constant? Are they essentially the same thing with the exception that a chemostat is run at steady state and a constant volume fermentor is run at exponential stage?
I am not sure I understand what you mean by: "a fed-batch fermentor with outflow" I have never heard this term. Chemostst is ruining as you wrote in a constant volume when the dilution rate is equal the growth rate in order to keep the population constant. Regarding a fed batch I think you are referring procedure which is done in some places in order to reduce the need to start with new inoculums each time. So if you have 100,000 L fermentor you harvest 80% of it and leaving 20% in the fermentor and filling with 80% new medium and after reaching the desired biomass you are repeating the harvest procedure.
Maybe this slide show can help you: http://slideplayer.com/slide/6854020/
Hello Sheenan. Good question. If we study the behavior of the fed-batch reactor you are suggesting by considering long time intervals (e.g., one week), we can see it as a continuous reactor with a low dilution rate. This means that after several days of operation, the reactor will reach a quasi-steady-state condition, similarly to a continuous reactor. However, at every feeding stage, the reactor will have a transient behaviour, similar to a batch reactor. So if for long operation intervals (several feeding stages in between) a quasi-steady state is achieved, a CSTR kinetics can be used to model growth in the reactor. This will imply that for small feeding volumes (or long retention times), we should expect larger substrate consumption and biomass concentrations, but lower productivities. The obliged reference for this topic is the classical book by Bailey and Ollis, Biochemical Engineering Fundamentals. Regards.
Well it is heaven and earth difference. To put it in very simple terms: first of all in chemostat you keep the volume constant where as the volume in Fed-Batch fermenter, it will keep on increasing. Secondly in chemostat specific growth rate will become equal to the dilution rate after some time (when equilibrium sets in), this will never happen in any batch system even in fed-batch systems and like these there are several differences in the two systems.
Dear Sheenan, I think you are referring to 'repeated fed-batch' system, during which you remove the amount of volume that you feed to keep the volume constant at all times. The difference is you don't have steady state as in chemostat. Therefore, your reactor equations will be different as well as the parameters of your kinetic model.
As Rogelio Valadez-Blanco mentioned, I have observed a 'quasi steady state' during my repeated fed-batch operation. The cell mass concentration was constant for a while, but not the other product/substrate concentrations.
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