Evaluation of Monod Kinetic Parameters

The equality of the specific growth rate and the dilution rate of the steady-state CSTF shown in Eq. (6.30) is helpful in studying the effects of various components of the medium on the specific growth rate. By measuring the steady-state substrate concentration at various flow rates, various kinetic models can be tested and the value of the kinetic parameters can be estimated. By rearranging Eq. (6.30), a linear relationship can be obtained as follows  

30) can be rearranged to give the following linear relationships, which can be employed instead of Eq. (6.35) for a better estimation of the parameters in certain cases. 

However, the limitation of this approach to determine the kinetic parameters is in the difficulty of running a CSTF. For batch runs, we can even use shaker flasks to make multiple runs with many different conditions at the same time. The batch run in a stirred fermenter is not difficult to carry out, either. Since there is no input and output connections except the air supply and the length of a run is short, the danger of contamination of the fermenter is not serious. 

For CSTF runs, we need to have nutrient and product reservoirs which are connected to the fermenter aseptically. The rate of input and output stream needs to be controlled precisely. Sometimes, the control of the outlet flowrate can be difficult due to the foaming or plugging by large cell aggregates. Since the length of the run should last several days or even weeks to reach a steady state and also to vary the dilution rates, there is always a high risk for the fermenter to be contaminated. Frequently, it is difficult to reach a steady state because of the cell s mutation and adaptation to new environment. 

Furthermore, since most large-scale fermentations are carried out in batch mode, the kinetic parameters determined by the chemostat study should be able to predict the growth in a batch fermenter. However, due to the significantly different environments of batch and continuous fermenters, the kinetic model developed from the CSTF runs may fail to predict the growth behavior of a batch fermenter. Nevertheless, the verification of a kinetic model and the evaluation of kinetic parameters by running chemostat is the most reliable method because of its constant medium environment. 

---