Fermentation bioreactors

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

In the approach followed in this invention [29], a biocatalytic agent converts the sulfur heterocycles into different molecules that do not exhibit the hydrophobic interactions. This is achieved by selectively cleaving carbon-sulfur bonds. The selectivity of the biocatalytic agent employed is limited to the carbon-sulfur bonds and no attack to the carbon-carbon skeleton was reported. Thus, it is expected that the proposed biocatalytic reduction of viscosity would not diminish the fuel value of the treated petroleum liquids. The biocatalyst employed consisted of the strain ATCC No. 53968 (see Section 20 and references therein), in an aqueous culture conventionally prepared by fermentation under aerobic conditions. The fermenting bioreactor is fed with a suitable nutrient medium, which comprises a conventional carbon source (dextrose and glycerol are recommended carbon sources. To confer maximal biocatalytic activity for the desired cleavage of organic C—S bonds, the bacteria was kept in a state of sulfur deprivation. 

Enzymatically coupled FETs have reached the stage of development where their application to practical sensing problems in various analytical fields is possible. Applications in the field of medical diagnostics are most frequent, although a few are used for the control of bioprocesses, for example, a fermentation bioreactor (12, 49). 

Figure 15.9-1 A schematic diagram of a fermenter (bioreactor) showing mass, heat, and work flows. The heat flow is generally to keep the reactor at constant temperature, and the work flow, which is usually small, is for stirring the reactor contents.

A solid-state fermentation bioreactor must fulfill one or more of the following functions ... 

Hochfeld, W. L., Producing Biomolectdar Substances with Fermenters, Bioreactors, and Biomolecular Synthesizers, Chap. 9, CRC Press/Taylor Francis Group, Boca Raton, FL, 2006. 

Bl Main fermentation bioreactor B2 Secondary fermentation bioreactor CJ Cooling jacket... 

Tempeh, a popular fermented food eaten as a meat substitute, is made in a solid-state fermentation bioreactor by cultivating the fungus Rhizopus oUgosporus on cooked soybeans. The fungus binds the soybeans into compact cakes that are fried and packaged to sell to the public. 

Researcher with algae fermentation bioreactor. (Volker Steger/Photo Researchers, Inc.)... 

Single-Cell Protein. Systems involving single-cell proteins are often very large throughput, continuous processing operations such as the Pmteen process developed by ICI. These are ideal for air-lift bioreactors of which the pressure cycle fermenter is a special case (50). 

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... 

Bioprocess Control An industrial fermenter is a fairly sophisticated device with control of temperature, aeration rate, and perhaps pH, concentration of dissolved oxygen, or some nutrient concentration. There has been a strong trend to automated data collection and analysis. Analog control is stiU very common, but when a computer is available for on-line data collec tion, it makes sense to use it for control as well. More elaborate measurements are performed with research bioreactors, but each new electrode or assay adds more work, additional costs, and potential headaches. Most of the functional relationships in biotechnology are nonlinear, but this may not hinder control when bioprocess operate over a narrow range of conditions. Furthermore, process control is far advanced beyond the days when the main tools for designing control systems were intended for linear systems. 

The down time of the bioreactor is a significant portion of the total fermentation time. 

Where yield coefficients are constant for a particular cell cultivation system, knowledge of how one variable changes can be used to determine changes in the other. Such stoichiometric relationships can be useful in monitoring fermentations. For example, some product concentrations, such as CO2 leaving an aerobic bioreactor, are often the most convenient to measure in practice and give information on substrate consumption rates, biomass formation rates and product formation rates. 

The production-scale fermentation unit, with a projected annual capacity of over50,000 tonnes was fully commissioned in 1980. The bioreactor (Figure 4.8) is 60 m high, with a 7 m base diameter and working volume 1,500 m3. There are two downcomers and cooling bundles at the base. Initial sterilisation is with saturated steam at 140°C followed by displacement with heat sterilised water. Air and ammonia are filter sterilised as a mixture, methanol filter sterilised and other nutrients heat sterilised. Methanol is added through many nozzles, placed two per square metre. For start-up, 20 litres of inoculum is used and the system is operated as a batch culture for about 30 h. After this time the system is operated as a chemostat continuous culture, with methanol limitation, at 37°C and pH 6.7. Run lengths are normally 100 days, with contamination the usual cause of failure. 

A reasonable size of bioreactor, based on transport and handling considerations, is 200 m3, with a working volume of 150 m3. If file fermentation time is 48 hours and down time for reuse about 24 hours, then the total batch time is 72 hours. 

As a rule of thumb, total investment of the fermentation plant is 50 dollars per litre of bioreactor. This means the total costs of investment are 200,000 x 50 = 10 million dollars. This figure includes all costs concerning engineering, fermentation equipment, recovery equipment, buildings land, etc. 

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. 

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