CSTR Bioreactor Operation

In this section we return to the mass balance equations on the cells [Equatlcm (9-75)] and substrate [Equation (9-76)) and consi r the case where the volumetric flow rates in and out are the same and that no live (i.e.. viable) cells enter the chemostat. We next define a parameter common to bioreactors called the dilution rate, D. The dilution rate is 

We now neglect the death rate, rj, and combine Equations (9-51) and (9-84) for steady-state operation to obtain the mass flow rate of cells out of the system, mt. 

An inspection of Equation (9-87) reveals that the specific growth rate of the How to control controlled by the operator by controlling the dilution rale D. 

Assuming that a single nutrient is limiting, cell growth is the only process contributing to substrate utilization, and that cell maintenance can be neglected, the stoichiometry is 

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Compare the cost of batch and CSTR (4 months per run) bioreactor operations. 

These infinitely variable problems in bioreactor operation are waiting to be solved. There have been relatively few systematic tests of the principles of interaction of mixed populations. Experimental work on the basis of the understanding from kinetic model theories should be encouraged by studies utilizing a CSTR, a CSTR cascade, or a CPFR. 

Apparently simple models are not always suitable for the description of the dynamics of bioreactor operations. As shown in Fig. 6.14, there are six classes of transient behavior of the CSTR ... 

CSTR behavior in case of more complex kinetics has been shown in Figs. 6.4 through 6.11 and 6.14 through 6.20. Alternative bioreactor operations (CPFR, NCSTR, RR, etc.) were represented in Sects. 6.4 through 6.8. 

A similar approach, starting with a material balance, can be used for the characterization of bioreactors operating in the continuous mode. Thus, for a perfectly mixed reactor, or continuous stirred tank reactor (CSTR), where the term of accumulation is zero at steady state and the liquid composition is uniform, the material balance for substrate A is given by Equation 7.7 ... 

A tubular bioreactor design with operational may lead to a CSTR, having sufficient recycle ratio for plug flow that behave like chemostat. The recirculation plug flow reactor is better than a chemostat, with maximum productivity at C, 3 g-m 3. Combination of plug flow with CSTR which behave like chemostat was obtained from the illustration minimised curve with maximum rate at CSf = 3 g-m-3. 

Figure 11.9 Different arrangements and modes of operation for membrane bioreactors Continuous Stirred Tank Reactor (CSTR) with recirculation arrangement (a), dead-end cell (b), tubular with entrapped enzyme (c).

Eq. 5.24 represents the model of steady-state operation of CSTR. As in the case of CPBR, it allows the determination of the steady-state X for any given combination of Mcat/F and can also be used for bioreactor design, since bioreactor dimensions will be determined from the concentration of biocatalyst that can be adequately handled in the bioreactor ... 

Once kii has been determined, the curve of reactor operation (X vs t) can be obtained from Eqs. 5.73 or 5.74. Values of Xi are obtained from Eqs. 5.16 or 5.24 for a certain enzyme load and feed flow-rate in the bioreactor. Eqs. 5.73 and 5.74 also allow bioreactor design (volume determination). In the case of CPBR, the volume of the catalytic bed can be directly determined from the amount of biocatalyst required, by dividing its mass by the apparent density of the biocatalyst bed, which is easily determined. In the case of CSTR, the volume of reaction can also be determined from the amount of biocatalyst required, by dividing its mass by the biocatalyst concentration, which is usually determined by hydrodynamic considerations. 

In principle the use of a well-stirred bioreactor in a continuous flow mode offers significant advantages over operation in a batch or semibatch mode, but the majority of bioreactors in industrial use are operated in the latter modes. However, the actual performance of single CSTR or a cascade of such reactors often fails to meet the expectations... 

Because activated sludge facilities have been utilized successfully for decades in the treatment of industrial wastewaters, and because of the similarity of the analysis of the peaformance of the constituent bioreactor to that for an individual CSTR operating with partial recycle of cells (see Section 13.2.4), we first consider how to develop steady state models of these bioreactors. We then proceed to matters related to the use of bioreactors for cultivation of animal and plant cells, including information pertinent to their susceptibility to damage in shear fields. We conclude with discussions of aspects of two interesting evolving... 

Membrane reactors were classically grouped according to the hydrodynam-ics/configuration of the system in CSTR and PFR types [106]. However, this proved vmable to comprise some commonly used types in UF, such as flat membranes or dead-end operated modules and multiphase bioreactors. A classification based on the contact mechanisms that bring together substrate and biocatalyst was thus proposed [110]. Thus, membrane reactors could be divided into direct contact, diffusion contact, and interfacial contact reactors. 

The total mass balance gives the rate of change of volume with inlet and outlet flow rates for a well-mixed constant-density system. A fed batch is a special case of a variable-volume CSTR operation It has been defined as a bioreactor with inflowing substrate but without outflow. For this system, the equation becomes... 

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