Fermentation, batch

In batch operation, the medium containing the substrate and nutrients is added at time zero. Then, the medium is sterilized and cooled before addition of the desired microorganism. Chemical agents are added to control pH, foam formation and contaminating bacteria, resulting in a minimal change in the net volume of the medium. 

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Activities associated with bioreactors include gas/hquid contacting, on-hne sensing of concentrations, mixing, heat transfer, foam control, and feed of nutrients or reagents such as those for pH control. The workhorse of the fermentation industry is the conventional batch fermenter shown in Fig. 24-3. Not shown are ladder rungs inside the vessel, antifoam probe, antifoam system, and sensors (pH, dissolved oxygen, temperature, and the like). Note that coils may lie between baffles and the tank wall or connect to the top to minimize openings... 

The manufacture of penicillin, for example, involves batch fermentation using... 

Inoculum A batch fermentation dial starts with an initial charge of cells. 

As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised and filled with fresh medium prior to inoculation. For some processes, addition of all the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the lifetime of batch cultures and thus product yields fed-batch cultures are considered further in Section 2.7.4. 

Conditions change with in batch fermentations but with distance along the... 

Typical units for productivity are kg m 3 h 1. Factors that influence productivity include the production time of the fermentation, the time required to dean and set up the reactor, the sterilisation time and the length of the lag phase of growth. Figure 2.2 shows how total productivity and maximal productivity can be calculated for a batch fermentation. The dedsion as to when the fermentation is terminated (maximum or total productivity) depends on the operating costs, which include the capacity of the fermentation vessel, energy costs and labour costs. 

Figure 3.1 illustrates the main patterns for batch fermentation process kinetics for type 1,2 and 3 processes. 

Batch fermentation is the most widely used method of amino add production. Here the fermentation is a dosed culture system which contains an initial, limited amount of nutrient. After the seed inoculum has been introduced the cells start to grow at the expense of the nutrients that are available. A short adaptation time is usually necessary (lag phase) before cells enter the logarithmic growth phase (exponential phase). Nutrients soon become limited and they enter the stationary phase in which growth has (almost) ceased. In amino add fermentations, production of the amino add normally starts in the early logarithmic phase and continues through the stationary phase. 

Fed-batch fermentations are batch fermentations which are fed continuously, or intermitantly, with medium without the removal of fluid. In this way the volume of the culture increases with time. 

One of the advantages of the fed-batch fermentation is the fact that the residual substrate concentration may be maintained at a very low level. This may result in a removal of catabolite repressive effects and avoidance of toxic effects of medium components. 

Despite the advantages of continuous cultures, the technique has found little application in the fermentation industry. A multi-stage system is the most common continuous fermentation and has been used in the fermentation of glutamic add. The start-up of a multi-stage continuous system proceeds as follows. Initially, batch fermentation is commenced in each vessel. Fresh medium is introduced in the first vessel, and the outflow from this proceeds into the next vessel. The overall flow rate is then adjusted so that the substrate is completely consumed in the last vessel, and the intended product accumulated. The concentration of cells, products and substrate will then reach a steady state. The optimum number of vessels and rate of medium input can be calculated from simple batch experiments. 

The culture can be used directly for the conversion of phenylpyruvic add to resting cells L-phenylalanine. Therefore, a batch process with resting cells can be carried out, with some glucose added for maintenance (fed-batch fermentation). Another approach is to harvest the cells from the fermentation broth and to use them in a separate bioreactor in higher concentrations than the ones obtained in the cell cultivation. An advantage of the last method can be that the concentration of compounds other than L-phenylalanine is lower, so that downstream processing may be cheaper. 

Figure 8.7 Fed-batch fermentation of phenylpyruvic acid to L-phenylalanine.

Batch. Fermentation run times are relatively short and the same bioreactor can be used for making several different products. 

Figure 3.7 shows the growth of R. rubrum in a batch fermentation process using a gaseous carbon source (CO). The data shown follow the logistic model as fitted by (3.14.2.11) with the solid lines, which also represent an unstructured rate model without any lag phase. The software Sigma Plot was used to fit model (3.14.2.11) to the experimental data. An increase in concentration of acetate in the prepared culture media did not improve the cell dry weight at values of 2.5 and 3 gT-1 acetate, as shown in Figure 3.7. However, the exponential growth rates were clearly observed with acetate concentrations of 0.5-2 g-F1 hi the culture media.

Table E.10.1. Microbial growth in a batch fermentation bioreactor...

Plate filters are suitable for filtration of batch fermentation broth accumulated biomass must be cleaned periodically. A rotary dram vacuum filter is used for a continuous system. 

Dining batch fermentation of Saccharomyces cerevisiae, other influential parameters can adversely influence the specific rate of growth, and inhibition can be caused either by... 

The size of beads was uniform and consistent, the mean size of beads with 3% alginate and based on measurement of 20 samples the mean value for the beads diameter was 4.85 mm, with a standard deviation of 0.3 mm and calculated variance of 0.1 mm. The standard deviation was less than 5%. The data for the batch fermentation experiment with 50gl 1... 

Fig. 8.6. Glucose concentration, cell density and production of ethanol in batch fermentation with initial concentration of 50 g-l 1 glucose versus time. Reprinted from Najafpour et al. (2004).18 Copyright with permission from Elsevier.

Table 10.1. Data sheet for batch fermentation, at constant agitation, experimental run 1...

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