Mixed Flow Fermentors

Method (a) uses all the data directly and presents it as a linear plot. This method is probably better, all round. 

Method (b) requires taking derivatives or slopes from experimental data, is more tedious, and is probably less reliable. 

For high C, thus put = 0 in the Monod equation. This gives Yq = A Cc, in which case the performance expression, Eq. 3, simplifies to 

2 MIXED FLOW FERMENTORS No Cells in Feed Stream, Cco = 0 

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Thus, optimum operations of a single mixed flow fermentor occurs when... 

Mixed Flow Fermentors for n = 1 649 the maximum production rate of cells and product is found to be... 

The alternative to batch mode operation is continuous operation. In the continuous mode there is a continuous flow of medium into the fermentor and of product stream out of the fermentor. Continuous bioprocesses often use homogenously mixed whole cell suspensions. However, immobilised cell or enzyme processes generally operate in continuous plug flow reactors, without mixing (see Figure 2.1, packed-bed reactors). 

The values of k a for CO, desorption in a stirred-tank fermentor, calculated from the experimental data on physically dissolved CO, concentration (obtained by the above-mentioned method) and the CO2 partial pressure in the gas phase, agreed well with the k a values estimated from the k a for O, absorption in the same fermentor, but corrected for any differences in the liquid-phase diffusivities [11]. Perfect mixing in the liquid phase can be assumed when calculating the mean driving potential. In the case of large industrial fermentors, it can practically be assumed that the CO, partial pressure in the exit gas is in equilibrium with the concentration of CO, that is physically dissolved in the broth. The assumption of either a plug flow or perfect mixing in the gas phase does not have any major effect... 

Repeating the procedure for all critical control variables yields actuators as follows coolant flow rate for temperature, ammonia flow rate for pH, air flow rate for DO and dissolved CO2, stirrer speed for homogeneity control in the fermentor, steam flow rate for heat sterilization temperature control and stirring duration for homogeneity in the mixing tank. 

Continuous-process control instruments may make measurements directly in a flowing stream or a batch process reactor such as a fermentor. This generally precludes any analytical operation on the sample, and direct sensing devices such as electrodes must be used. If a sample dilution, temperature control, or reagent addition is required, or measurements are made with nonprobe-type instruments, then a small fraction of the stream is diverted into a test stream where reagents may be mixed continuously and automatically with the sample, and the test measurement is made. The sample may be passed through a filter prior to measurement. 

Cell recycle fermentors consist of two main units a vessel where the biomass is allowed to grow, and a membrane separation unit (as in Figure 7.40). Vessels are usually designed to insure a uniform concentration of nutrients and pH throughout the whole volume. Due to complete mixing, process control and stability of the microbial slurry are not difficult to achieve.88 After anaerobic stabilization, when the biomass is well developed, the reactor biomass is pumped to the UF unit where solid-liquid separation occurs. The sludge is flushed back to the reactor. In most cases, the flow rate of nutrient feed is kept equal to the permeate flow rate thus keeping a constant liquid level in the anaerobic reactor. 

Recently, Lubbert and Larson (1990) analyzed the local mixing behavior in bubble columns and in air-lift fermentors utilizing a heat pulse-probe experiment. They considered the spreading of an originally narrowly distributed clump along the principle flow direction. Based on theory, the width of the spreading cloud (i.e. standard deviation) can be described by ... 

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