Fermentation processes problems

Fermentation. Much time and effort has been spent in undertaking to find fermentation processes for vitamin C (47). One such approach is now practiced on an industrial scale, primarily in China. It is not certain, however, whether these processes will ultimately supplant the optimized Reichstein synthesis. One important problem is the instabiUty of ascorbic acid in water in the presence of oxygen it is thus highly unlikely that direct fermentation to ascorbic acid will be economically viable. The successful approaches to date involve fermentative preparation of an intermediate, which is then converted chemically to ascorbic acid. 

Fermentation Processes. The efficient production of penicillin, yeasts, and single-ceUed protein by fermentation requires defoamers to control gas evolution during the reaction. Animal fats such as lard [61789-99-9] were formerly used as a combined defoamer and nutrient, but now more effective proprietary products are usually employed. Defoamer appHcation technology has also improved. For example, in modem yeast production faciHties, the defoamers are introduced by means of automatic electrode-activated devices. One concern in the use of defoamers in fermentation processes is the potential fouHng of membranes during downstream ultrafiltration (qv). SiHcone antifoams (43,44) seem less troubled by this problem than other materials. 

A major breakthrough in the fermentation process came in 1916 - 1920 when it was found that Aspergillus niger grew well at pH values below 3.5, producing citric add in days rather than weeks. The faster incubation and highly add conditions (often below pH 2.0) also served to minimise potential problems caused by contamination. 

Bakshi and Stephanopoulos (1994b) have applied the above procedure to a fed-batch fermentation process. The problem involved 41 sets of batch records on 24 measured variables. Of these variables only very few were found by the decision tree to be relevant, and yield rules such as the following for guiding the diagnosis or control of a fermentor. 

Finally, ion chromatography is sometimes used for process applications, allowing for the tracking of the manufacturing process in order to optimize process variables and to allow for better control of process parameters. One example of this is the application of ion chromatography to the analysis of fermentation broths. Here ion chromatography is used both to measure the level of ionic nutrients in the fermentation broth in order to control the fermentation process and also to measure the level of fermentation by-product ions which may be indicative of problems with the fermentation process. 

Probably the major problem in the scale-np of fermentation processes lies in maintaining aeration efficiency to aerobic cultnres. Aeration is normally achieved by sparging with air and the rate determining step in a non-viscons fermentation is the... 

Since proteins strongly adsorb at interfaces, very low concentrations (as low as 1 mg/L) can influence foaming. This can cause foaming where it is not desired, such as where it causes operational problems in fermentation processes [844]. Additives with fatty-acid chains generally tend to be capable of stabilizing foams, whereas those with unsaturated fatty-acid chains generally tend to destabilize foams [820]. Other food defoamers that have been used include oils, glycols and siloxanes [486,844]. Some commercial food defoamers are listed in Ref. [845],... 

Another problem with conventional fermenters concerns foaming. In traditional systems, the introduction of large quantities of gas into the vigorously agitated fermentation liquor often produces great quantities of foam in the reaction vessel. Biological reactors are particularly susceptible to foaming because of the surfactant properties of most biomolecules. This foam severely limits the usable volume of the vessel and can render the fermentation process inoperable and microbially contaminated when the gas flow exit lines become filled with foam. All of these problems have a substantially adverse influence upon the yield and cost-eflectiveness of conventional fermentation processes. 

Aerobic fermentation processes also require a continuous supply of large quantities of air, typically on the order of one volume of air per volume of liquid per minute, VVM. Sterilization of this air is mandatory in almost all fermentations. Absolute filter cartridges of polymeric membranes are now used almost exclusively in the fermentation industry. Relatively small units have replaced the large depth filters used in the past. Still, water and particulates pose a major problem for filters thus requiring the use of prefilters and traps to remove these contaminants before they reach the absolute filter. Parallel installation of the filters prevents a total shutdown of the fermentation process in the event of filter clogging. 

Space-time yield (STY) sets the capital costs of the production facility and an STY of 100 g I, 1 d 1 has often been mentioned as the minimum for the profitable production of a building block of intermediate complexity. Fermentation processes are often much less productive, due to regulation (inhibition) and toxicity problems. 

The butanols and their methyl and ethyl ethers have several advantages as oxygenates over methanol and ethanol in gasoline blends. Their energy contents are closer to those of gasoline the compatibility and miscibility problems with petroleum fuels are nil excessive vapor pressure and volatility problems do not occur and they are water tolerant and can be transported in gasoline blends by pipeline without danger of phase separation due to moisture absorption. Fermentation processes (Weizmann process) have been developed for simultaneous production of 1-butanol, 2-propanol, acetone, and ethanol from... 

As mentioned earlier, a controversial issue that developed when fermentation ethanol was first marketed as a motor gasoline component in modern times concerned the amount of energy consumed in the fermentation process. The basic problem with conventional yeast fermentation of corn sugars and purification was that more energy can be consumed to manufacture a unit of ethanol than the energy contained in that unit. The problem was compounded in the... 

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