SOLUTION—FERMENTATION PROBLEMS

KqO Gas-liquid mass transfer coefiScient based on liquid concentrations MJ Megajoule 

K factor Ratio of horsepower with gas to power with gas ofif at 

MIZSR Maximum impeller zone shear rate 

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In particular, aspects requiring further studies include partial dehydration and the consequences of botrytization the development of solution to problems associated with alcoholic and malolactic fermentation and a clear understanding of critical processes associated with maturation. 

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

The study of the reactions with the participation of glycosyl bonds is important not only for the theoiy of carbohydrates structure and reactional ability of carbohydrates. They represent a significant interest and solution for a number of important problems of organic, bioorganic chemistry, and molecular biology, fermentative catalysis, since the glycosyl bond is one of the most important structural elements of many biologically active compounds. 

It is frequently desirable, particularly in the field of waste-water treatment, to operate a continuous fermenter at high dilution rates. With a simple stirred-tank this has two effects—one is that the substrate concentration in the effluent will rise, and the other is that such a system in practice tends to be unstable. One solution to this problem is to use a fermenter with a larger working volume, but an alternative strategy is to devise a method to retain the biomass in the fermenter whilst allowing the spent feed to pass out. There are several methods by which this may be achieved (see Fig. 5.60), and the net effect is the same in each case, but the analysis might... 

The sodium sulfite oxidation technique has its limitation in the fact that the solution cannot approximate the physical and chemical properties of a fermentation broth. An additional problem is that this technique requires high ionic concentrations (1 to 2 mol/L), the presence of which can affect the interfacial area and, in a lesser degree, the mass-transfer coefficient (Van t Riet, 1979). However, this technique is helpful in comparing the performance of fermenters and studying the effect of scale-up and operating conditions. 

The fermentability of the solution gave good results. The achieved ethanol yields were about 90%, slightly above those obtained with a reference sugar solution, showing that baker s yeast could adapt to the pretreated liquor and ferment the glucose to ethanol without problems. 

There is no current commercial biologic process for the production of succinic acid. In past laboratory systems, when succinic acid has been produced by fermentation, lime is added to the fermentation medium to neutralize the acid, yielding calcium succinate (2). The calcium succinate salt then precipitates out of the solution. Subsequently, sulfuric acid is added to the salt to produce the free soluble succinic acid and solid calcium sulfate (gypsum). The acid is then purified with several washings over a sorbent to remove impurities. The disposal of the solid waste is both a directly economic and an environmental concern, as is the cost of the raw materials. Some key process-related problems have been identified as follows (1) the separation of dilute product streams and the related costs of recovery, (2) the elimination of the salt waste from the current purification process, and (3) the reduction of inhibition to the product succinic acid on the fermentation itself. Acetic acid is also a byproduct of the fermentation of glucose by Anaerobiospirillium succiniciproducens almost 1 mol of acetate will be produced for every 2 mol of succinate (3). Under certain cultivation conditions by a mutant Escherichia coli, lesser amounts of acetate can be produced (4,5). This byproduct will also need to be separated. 

Conclusion areas for future research. Mixing in stirred reactors is no longer the empirical operation it used to be, ("mostly art and very little science" (153). For instance, Oldshue summarized useful rules for the scale-up of fermenters (153). However, several current problems are still waiting solution. These were reviewed in an excellent paper by Kipke (154). Future research should be directed towards... 

One would think a solution to increase the productivity would be to use oxygen enrichment, not just during the choke-out period but also during the remainder of the fermentation in order to sustain the productivity. This does not work because of broth viscosity and gas holdup problems. In highly mycelial systems, a 15% increase in cell mass doubles the viscosity. The volumetric oxygen mass transfer coefficient and the bubble rise velocity—... 

A fermentative or biocatalytic procedure for 2KLG calls for a completely different approach to the DSP of the latter and possibly also for the conversion of 2KLG into ASA. The basic problem is that 2KLG is dissolved in the culture supernatant as a salt, due to the necessity to titrate the culture with base to maintain neutrality. The conversion of 2KLG into ASA, in contrast, requires the free acid. Traditional solutions, such as spray-drying and acidification with sulfuric acid [170] and evaporative crystallization [171], are energy intensive and coproduce an equivalent of salt, which is, parenthetically, one of the objections against the Reichstein process. 

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