Agitated Fermentors Research Articles

Polygalacturonase Production by Aspergillus sp. in Air-Lift and Agitated Fermentor

Polygalacturonase production under different shear stress environments by Aspergillus sp. was studied. It was found that the rate of enzyme production in the stirred tank fermentor decreased with increasing the stirrer speed in the range 300-750 rpm. On the other hand, in a split cylinder air-lift fermentor, the rate of polygalacturonase production slightly increased with increasing in air rate from 1.5 to 2 v.v.m (volume air/culture volume/minute). The maximum enzyme titres at the end of the cultivation period in the airlift fermentor were 35 unit/ml and at least twice of that obtained in agitated fermentors. Measurement of main hyphal length in agitated and air-lift fermentors suggested break up of the mycelia in the higher shear environment of stirred fermentor especially at the higher agitation rates. The similarity in the trend of the enzyme production and main hyphal length suggested a possible relationship between the morphology and productivity of the Aspergillus sp. used in the present study.

Glycerol production by a novel osmotolerant yeast Candida glycerinogenes.

Candida glycerinogenes, an osmotolerant yeast isolated from a natural sample in an environment of high osmotic pressure, had a modest sugar-tolerance and an extremely high glycerol productivity. The optimum conditions for glycerol formation by C. glycerinogenes were a temperature of 29-33 degrees C and a pH of 4-6. The optimum medium for glycerol production consisted of 230-250 g glucose/l, 2 g urea/l and 5 ml corn steep liquor/l (55-65 mg phosphates/l); the pH was not adjusted. The highest yield of glycerol was 64.5% (w/w) based on consumed glucose from 240 g glucose/l, and the highest concentration of glycerol was 137 g/l from 260 g glucose/l. These results were obtained by using a 30-l agitated fermentor under optimal fermentation conditions. In ten batch-fermentations carried out in a 50,000-l airlift fermentor, an average yield of glycerol of 50.67% (w/w) and an average glycerol concentration of 121.9 g/l were obtained from an average 240.6 g glucose/l.

Semicontinuous production of lipase by Acinetobacter radioresistens in presence of nonwoven fabric.

The effect of a hydrophobic nonwoven fabric on the lipase production by Acinetobacter radioresistens was investigated with semicontinuous culture. The fermentation medium contained n-hexadecane as the carbon source. The nonwoven fabric was made from nylon 6 and coated with an acrylic resin. Equipping the nonwoven fabric around the baffles of a 2.5-L agitated fermentor could provide a fine dispersion of n-hexadecane, thus enhancing lipase production. The improvement on lipase yield by using the nonwoven fabric was found to be comparable to that of using an emulsifier (gum arabic). Compared with the corresponding culture in the absence of nonwoven fabric, the employment of the nonwoven fabric could significantly enhance both lipase yield and volumetric productivity.

Effect of lard oil, olive oil and castor oil on oxygen transfer in an agitated fermentor

Adding lard oil, olive oil or castor oil into a baffled and agitated fermentor decreased the volumetric oxygen transfer coefficient (KLa) in the low concentration range. However, KLa was increased when concentration reached 0.25% (v/v) at 400 rpm. Experimental results indicated that 1% (v/v) olive oil was as good as 0.1% (v/v) polypropylene glycol when added to a yeast fermentation.

Oxygen transfer kinetics of riboflavin fermentation by Ashbya gossypii in agitated fermentors

Effects of agitation and aeration rates on volumetric oxygen transfer coefficient and oxygen uptake rate of a riboflavin broth containing Ashbya gossypii were investigated in three batch, sparged, and agitated fermentors having the working volumes of 0.42, 0.85, and 2.5 l. The change of oxygen uptake rate with time at 250 rev min −1 stirring and 1 4 vvm aeration rates was shown. The volumetric oxygen transfer coefficients and maximum oxygen uptake rates obtained have been correlated to mechanical power inputs per unit volume of the fermentation broth and the superficial air velocities.

Micromixing in fermentors: Metabolic changes in Saccharomyces cerevisiae and their relationship to fluid turbulence

Even when microorganisms are grown in highly agitated fermentors, calculation predicts a mismatch between the microscale of the turbulence (where the smallest eddy is typically 50-300 microm diameter) and the cellular dimensions (1-5 microm). The cell thus spends substantial portions of time in an apparently stagnant eddy, depleted of nutrients. The local fluid microscales were measured in a laboratory fermenter to confirm this. Using S. cerevisiae in continuous culture, it is shown that the local microscales influence cell metabolism dramatically. The issues addressed in this study are thus micromixing and microsegregation of reactants and how they influence cell yield.

Improvements In Multi‐Turbine Mass Transfer Models

AbstractMathematical modeling approaches are being developed to better understand and describe the overall performance of large‐scale agitated fermentors. These new approaches are based upon subdividing the fermentor into various mixing cells, or stages. The further development of these models requires information on the power input per stage, its effect on mass transfer within the stage, fluid mixing patterns between stages, and the distribution of gas in the fermentor stages. The following discussion presents data and comments related to these topics for aerobic fermentations of low to medium viscosity.

Scaling oxygen mass transfer in agitated fermentors

There are many scaling formulas that predict the oxygen mass transfer coefficient as k(L)xa = constant x (Hp/V)(alpha)Vs(beta). Exponents alpha and beta frequently are scale dependent themselves. A general formula has been derived from the work of Calderbank,(1) Miller,(2) and Tilton,(3) resulting in k(L)xa = C(1) phi + C(2) log (Pm/V) phi where phi equals the gas-holdup fraction and Pm/V equals the effective mechanical power input per unit of volume. This formula is consistent with the formula of Westerterp(4) modified by Miller.(2) Gas holdup can be predicted in several ways. Gas-sparged isothermal expansion power input, used for predicting phi, demonstrates that scaling can be done by using either superficial air velocity or volume per volume per minute for aeration.The importance of mixing in replenishing oxygen at the boundary layers of microorganisms will be assessed and compared with the k(L)xa as the oxygen transfer rate-limiting step.

Effect of shaking speed and type of closure on shake flask cultures.

Growth of microorganisms and biosynthesis of microbial products in shake flasks may be limited by operating conditions which provide inadequate supplies of oxygen. Methods are described for meeting the oxygen requirements of test organisms by using standard baffled flasks with pad-type closures and shaking at relatively high speeds. Growth of Escherichia coli B in a rich medium and production of candidin by Streptomyces viridoflavus were the test systems used. Flasks shaken at 230 to 385 rev/min gave sulfite oxidation rates of 1 to 8 mmoles of oxygen per liter per min over a useful working volume range (40 to 150 ml in 300-ml flasks). These rates are as high as those obtained in agitated fermentors under usual operating conditions.

Effect of Shaking Speed and Type of Closure on Shake Flask Cultures

Growth of microorganisms and biosynthesis of microbial products in shake flasks may be limited by operating conditions which provide inadequate supplies of oxygen. Methods are described for meeting the oxygen requirements of test organisms by using standard baffled flasks with pad-type closures and shaking at relatively high speeds. Growth of Escherichia coli B in a rich medium and production of candidin by Streptomyces viridoflavus were the test systems used. Flasks shaken at 230 to 385 rev/min gave sulfite oxidation rates of 1 to 8 mmoles of oxygen per liter per min over a useful working volume range (40 to 150 ml in 300-ml flasks). These rates are as high as those obtained in agitated fermentors under usual operating conditions.