Chemostat kinetics

Chemostat kinetics Weighted divergence as a function of square wave frequency for eft) at the grid point (1, 0 20). 

Table 12.7 Chemostat Kinetics Results from Model Adequacy Tests Assuming af. is Known (yftest) Performed at a=0.0I Level of Significance...

In a chemostat and biostat or turbidostat, even with differences in the supply of nutrients and/or fresh media, constant cell density is obtained. The utilisation of substrate and the kinetic expressions for all the fermentation vessels are quite similar. It is possibile to have slight differences in the kinetic constants and the specific rate constants.3,4 Figure 5.9 shows a turbidostat with light sources. The system can be adapted for photosynthetic bacteria. 

The performance data for plug versus mix reactor were obtained. The data were collected as the inverse of qx vs inverse of substrate concentration. Table E.1.1 shows the data based on obtained kinetic data. From the data plotted in Figure E.1.1, we can minimise the volume of the chemostat. A CSTR works better than a plug flow reactor for the production of biomass. Maximum qx is obtained with a substrate concentration in the leaving stream of 12g m 3. 

Microbial kinetics can be quite complex. Multiple steady states are always possible, and oscillatory behavior is common, particularly when there are two or more microbial species in competition. The term chemostat can be quite misleading for a system that oscillates in the absence of a control system. 

As a third example let us consider the growth kinetics in a chemostat used by Kalogerakis (1984) to evaluate sequential design procedures for model discrimination in dynamic systems. We consider the following four kinetic models for biomass growth and substrate utilization in the continuous baker s yeast fermentation. 

Linardos, T., "Kinetics of Monoclonal Antibody Production in Chemostat Hybrid-oma Cultures", Ph D. thesis, Dept, of Chemical Petroleum Engineering, University of Calgary, AB, Canada, 1991. 

Fig. 2 Steady states A (stable) and B (unstable) for a chemostat with inhibition kinetics.

Tros, M T. N. P. Bosma, G. Schraa, and A. J. B. Zehnder, Measurement of minimum substrate concentration (Smin) in a recycling fermentor and its prediction from the kinetic parameters of Pseudomonas sp. strain B13 from batch and chemostat cultures , Appl. Environ. Microbiol., 62,3655-3661 (1996). 

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. 

You are going to cultivate yeast, Saccharomyces cerevisiae, by using a 10 m -fermenter your company already owns. You want to find out the amount of ethanol the fermenter can produce. Therefore, a chemostat study was carried out and the Monod kinetic parameters for the microorganism grown in the glucose medium at 30°C, pH 4.8, were found to be Ks = 0.0025 g/L and /imax = 0.25 h-1. The ethanol yield (YP/S) is 0.44 (g/g) and cell yield (Yx/S) is 0.019 (g/g). The inlet substrate concentration is 50 g/L-... 

Several special terms are used to describe traditional reaction engineering concepts. Examples include yield coefficients for the generally fermentation environment-dependent stoichiometric coefficients, metabolic network for reaction network, substrate for feed, metabolite for secreted bioreaction products, biomass for cells, broth for the fermenter medium, aeration rate for the rate of air addition, vvm for volumetric airflow rate per broth volume, OUR for 02 uptake rate per broth volume, and CER for C02 evolution rate per broth volume. For continuous fermentation, dilution rate stands for feed or effluent rate (equal at steady state), washout for a condition where the feed rate exceeds the cell growth rate, resulting in washout of cells from the reactor. Section 7 discusses a simple model of a CSTR reactor (called a chemostat) using empirical kinetics. 

Vadstein, O., and Olsen, Y. (1989). Chemical composition and phosphate uptake kinetics ofhmnetic bacterial communities cultured in chemostats trader phosphorus hmitation. Limnol. Oceanogr. 34(5), 939-946. 

We take as the model that of the simple chemostat of Chapter 1, with input nutrient S(t) and organism x t) growing on that nutrient, and add two predators on x which we label y and z- It is assumed that both the nutrient uptake from the lowest level and the predation from the highest level follow Michaelis-Menten or Monod kinetics. The use of the Monod formulation has already been discussed for the consumption of the nutrient. That the same format should apply in the case of a predator feeding on prey is not immediately clear. This formulation is one of a general class known as a Holling s type-II functional responses [Hoi]. A nice discussion can be found in [MD, p. 5], which we repeat here. 

A mass balance for organisms and substrate around a chemostat combined with these kinetic relationships yields the following two equations ... 

More extensive discussions of the theoretical aspects of chemostat culture have been published elsewhere (e.g. Herbert et al, 1956 Pirt, 1975 Bailey Ollis, 1977). Many of the theoretical principles apphed to microbial chemostat cultures can be applied successfully to animal cell cultures, although there are a number of instances where the behaviour of animal cells has been reported to deviate from the models used to describe microbial growth kinetics (Tovey, 1980 Boraston et al, 1984 Miller et al., 1988). 

The global stoichiometry changes with operating conditions and feed composition kinetics and stoichiometry obtained from steady-state (chemostat) data cannot be used reliably over a wide range of conditions, unless fundamental models are employed. 

Chemostat with Empirical Kinetics Using the CSTR equation (7-54) for a constant-volume single reaction [Eq. (7-147)], the substrate, biomass, and product material balances are... 

The preferred reactor for kinetics is the chemostat, but semibatch reactors are more often used owing to their simpler operation. 

A second type of culture described by Monod kinetics is the continuous culture, in which a chemical is constantly fed into a vessel and both microbial cells and the chemical are constantly lost from the vessel at a given rate. This culture is often called a chemostat when operated under steady-state conditions. Like the batch culture, a continuous culture may be a useful model of certain environmental systems, such as lakes receiving continuous discharges of pollutants. Continuous cultures are common in industrial processes as... 

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