Stirred fermentations

A strain of Azotobacter vinelandii was cultured in a 15 m3 stirred fermenter for the production of alginate. Under current conditions the mass transfer coefficient, kLa, is 0.18 s. Oxygen solubility in the fermentation broth is approximately 8 X 10 3 kgm-3.9 The specific oxygen uptake rate is 12.5 mmol g 1 h. What is the maximum cell density in the broth If copper sulphate is accidentally added to the fermentation broth, which may reduce the oxygen uptake rate to 3 mmol g 1 h 1 and inhibit the microbial cell growth, what would be the maximum cell density in this condition ... 

The use of stirred fermenters with automatic control of the culture environment is the most suitable technique to evaluate bacterial or fungal kinetics. Cultures can be operated in discontinuous mode (batch cultures). 

Citric acid fermentation of cane-molasses is by submerged fermentation in a 21 biostat (B. Braun) stirred fermenter. A strain of Aspergillus niger is the most widely used for commercial production. A. niger is also highly recommended in the present study, which can obtained from the American Type Culture Collection, Rockville, Maryland, USA. Molasses... 

Citric acid fermentation of cane-molasses by submerged fermentation in 21 B. Braun stirred fermenter (working volume 21) is performed. A strain of A. niger ATCC 11414 is... 

An ideal stirred fermenter is assumed to be well mixed so that the contents are uniform in composition at all times. Another ideal fermenter is the plug-flow fermenter, the analysis of which is analogous to the ideal batch fermenter. 

However, the limitation of this approach to determine the kinetic parameters is in the difficulty of running a CSTF. For batch runs, we can even use shaker flasks to make multiple runs with many different conditions at the same time. The batch run in a stirred fermenter is not difficult to carry out, either. Since there is no input and output connections except the air supply and the length of a run is short, the danger of contamination of the fermenter is not serious. 

Configuration of a typical mechanically stirred fermenter. (After Moo-Young, 1986.)... 

Whilst a surface culture may be grown for a month or even longer, a shake culture may be grown for 10-14 days and a stirred fermentation for an even shorter period of time. Methods have been developed for continuous culture in which fresh sterile medium is added to a growing fermentation whilst spent medium containing the metabolites is removed. On the laboratory scale this is quite difficult to maintain sterile but it is used commercially. 

To avoid the limitation of plant sources, several groups initiated studies of tissue culture from the TW plant as a source of triptolide 1. Kutney s group first studied TW tissue culture. The shake-flask and stirred fermenter batch cultures of TW cell tissue line TRP 4a grown on modified PRL-4 medium were harvested after 6 weeks. Cell cultures were extracted and separated by column chromatography. Compounds 1 and 2 were separated in yields that were 3 and 16 times greater, respectively than those observed in the plant itself. Additionally, dehydroabietic acid, celastrol, oleanoic acid, polpunonic acid, fl-sitosterol and other compounds were separated from the culture [104]. Zhu and his group cultivated tissue induced from TW leaves and stems, on the 67-v medium containing 0.1 mg/L, 2,4-D and 0.1 mg/L KT for 7 weeks. After separation of the cultivated material, the yield of 1, 2 and 4 was 12 times more than that in the plant (9.184 mg/L) [105]. 

Fermenter studies were carried out in a New Brunswick continuous culture apparatus with 15-liter stirred fermenter jars for culture vessel and nutrient reservoirs and a 20-liter carboy for a harvest vessel. Temperature of the culture was maintained at 28°-29°C. Impeller speed was kept at 120 r.p.m. with a 3-inch diameter set of four impeller blades low in the culture, and a second impeller just above the liquid level to aid in foam control. A few drops of Dow Coming Antifoam AF at 25 mg./ml. (emulsion) were added manually as required to control foam. The rate of aeration was 1 to 3 liters per minute. Contamination through the impeller shaft port was prevented by a loose fitting sleeve through which live steam was continually passed (10). Samples taken from the fermenter were streaked on potato dextrose agar, and Bacto plate count agar, incubated for 7-10 days and inspected for contamination. 

Laboratory studies on continuous fermentation of wort by brewers yeast demonstrated that satisfactory beers could be produced only when a number of stirred fermenters were used in series (cascade system) or in tubular (tower) fermenters (Chapter 19). In both cases satisfactory throughputs were only obtained by ensuring a high concentration of yeast remained in the system. To achieve this, in a cascade system, yeast was recycled from the outflow back into the fermenter. Under such conditions in a single vessel homogeneously mixed system at steady state we have ... 

Morao A, Maia Cl, Fonseca MMR, Vasconcelos JMT, Alves SS. (1999) Effect of antifoam addition on gas-liquid mass transfer in stirred fermenters. Bioprocess Eng., 20 165-172. 

Most of the enzyme is formed during the main tank fermentation process, which is carried out in large, aerated, and stirred fermentation tanks ranging from 40 m to several hundred cubic meter in volume [2]. 

Another relevant parameter for continuous, stirred fermenter operation is the identification of the dilution rate which maximizes cell production. Since the volumetric cell productivity can be expressed as... 

Tabera, J., Local gas hold-up measurement in stirred fermenters. 1 Description of the measurement apparatus and screening of variables, Biotechnol. Tech. 4(5) (1990), 299-304. 

Airlift bioreactors are highly energy efficient relative to stirred fermenters, yet the productivities of both types are comparable. Heat and mass transfer capabilities of airlift reactors are at least as good as those of other systems, and airlift reactors are more effective in suspending solids than are bubble columns. For optimal gas-liquid mass transfer... 

Gunyol, O. (2014) CFD of gassed, stirred fermenters, PhD thesis. Delft University of Technology. 

Dion, W. M., A. Carilli, G. Sermonti, and E. B. Chain (1954). The effect of mechanical agitation on the morphology of Penicillium chrysogenum Thom in stirred fermenters. Rend. 1st Super. Sanita, 17, 187-205. 

Manfredini, R., V. Cavallera, L. Marini, and G. Donati (1983). Mixing and oxygen transfer in conventional stirred fermenters, BiotechnoL Bioeng., 25, 3115-3131. 

In fermentation reactors, microorganisms produce enzymes (and other metabolic products) on a large scale. The enzymes are sold to companies producing, for example, detergent powders. Now and then, severe foaming appears in the stirred fermenters, which may cause loss of enzymes upon mechanical removal of the foam. 

Morud KE (1994) Turbulent two-phase flow in bubble columns and stirred fermenters. Dr Ing thesis, PhD Thesis, Telemark College, Porsgrunn, Norway... 

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