Mixing in Bioreactors

A bioreactor is a typical three-phase reactor. Chapman et al. (1983a, b, c, d) carried out a systematic investigation on the different mixing processes of importance in stirred three-phase reactors. This was followed by various studies on gas-liquid mixing and SOM-liquid mixing (solid suspension), as outlined in Chapter 7A. 

Mixing time is a vital parameter affecting the efficiency of a bioreactor. The local concentrations of nutrients, toxins, dissolved oxygen, etc. are all dictated by the mixing process. A low mixing time ensures quick response to any additions (pH equalization, uniform distfibution of nutrients, etc.). This results in uniformity of concentrations of aU the important ingredients participating in the bioprocess. 

A peak in the property that is being measured is observed at completion of each flow loop at the location of the probe. Khang and Levenspiel s (1976) alterion of five circulations (or five peaks in Fig. 7B.16) has been widely used to obtain the mixing time (Nienow 1998). Sardeshpande et al. (2(X)9) measured both mixing time 

FIGURE 7B.16 Typical probe response to a pulse input in a stirred reactor. (Reproduced from Khang and Levenspiel (1976) with permission from Elsevier. 1976, Elsevier.) 

STIRRED TANK REACTORS FOR CELL CULTURE TECHNOLOGY 

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Finally, the effect of structured models due to imperfect mixing in bioreactors upon product formation, yield, and conversion will be mentioned here. It was shown by Oosterhuis (1984) that Vp can be considered to consist of two parts = residence time in aerated compartment and = (Vi + V2)/ fp)] ... 

P., and Toye, D. (2014) CFD-based compartment model for description of mixing in bioreactors. Chem. Eng Scl,... 

Larsson, G., and S. O. Enfors (1988). Studies of insufficient mixing in bioreactors effects of limiting oxygen concentrations and short term oxygen starvation on Penicillium chrysogenum. Bioprocess. Eng., 3(3), 123-127. 

Biichs J, Zoels B (1999) Evaluation of the Maximiun Specific Power Consumption in Shaking Bioreactors, Proceedings of 3th International Symposium on Mixing in Industrial Processes (ISMlP-3) 19-22 Sept 1999 Japan... 

If substrate inhibition exists, a well-mixed bioreactor is desirable. Mixing in three-phase fluidized bed bioreactors can be increased by adding an external recycle loop, by inserting a draft tube in the reactor, or by decreasing the height to diameter ratio. 

Mann, R., D. Vlaev, V. Lossev, S. D. Vlaev, J. Zahradnik, and P. Seichter (1997). A network of zones analysis of the fundamentals of gas liquid mixing in an industrial stirred bioreactor. Recent Progres dans le Genie des Procedes 11, 223-230. 

An alternative method for coupling enzymes is to employ a mixed enzyme bioreactor Pezzotti and Therisod [60] reported a bienzymatic system in which alcohol oxidase and peroxidase were coupled to effect the enantioselective oxidation of the sulfide thioanisole (Scheme 3.4). Here, the peroxidase from Coprinus dnereus was mixed with a crude extract of Pichia pastoriz alcohol oxidase and the two enzyme mixture was successfully used to convert gram quantities of thioanisole enantiose-lectively to S-methyl-phenyl-sulfoxide with an enantiomeric excess of 75%. 

Most biopolymers are produced as extracellular metabolites by fermentation in bioreactors leading to special technical problems caused by the very viscous solutions that make mass transfer and mixing in the fermentation fluids difficult. Large volumes of water and solvents are needed for dilution and extraction, respectively. 

Venkat, R.V., Study of hydrodynamics due to turbulent mixing in animal cell microcarrier bioreactors, Dissertation of The Ohio State University, 1995... 

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