Improvement of foam breaking and oxygen-transfer performance in a stirred-tank fermenter

This study examined a stirred-tank fermenter (STF) containing low-viscosity foaming liquids with an agitation impeller and foam-breaking impeller mounted on the same shaft. Results showed that the performance of the foam-breaking impeller can be improved by changing a conventional six-blade turbine impeller into a rod impeller as the agitation impeller. The volumetric oxygen-transfer coefficient, k _L a, in the mechanical foam-control method (MFM) using a six-blade vaned disk as the foam-breaking impeller in the STF with the rod impeller was approximately five times greater than that of the chemical foam-control method (CFM) adding an anti-foaming agent in the STF with the six-blade turbine impeller. Application of the present method to the cultivation of Saccharomyces cerevisiae K-7 demonstrated that the cultivation time up to the maximum cell concentration was remarkably shorter than that achieved using a conventional CFM.     

Design and performance characteristics of a continuous multistage tower fermentor

The design of a continuous multistage tower fermentor is described. The fermentor consists of five stages separated by perforated plates. Each stage includes mechanical mixing provided by two disc turbine impellers and has its own impeller shaft with bearing assembly and flexible coupling that enables the operation of an arbitrary number of stages. The normal operation of this system enables the co-current flow of gas and liquid, but the system can function countercurrently as well. The purpose of this study was to examine the hydrodynamic performance, i.e., the pressure gradient along the tower, the mixing time, gas holdup, the residence lime distribution of the continuous phase, the value of the backflow coefficient, and the oxygen transfer rate under conditions usually used during fermentations. From the interrelations between parameters influencing the proper performance of this system, an optimal design of plate geometry for processes requiring high oxygen transfer rate was formulated.     

Rotating drum fermentor for plant cell suspension cultures

A rotating drum fermentor designed for plant cell suspension cultures was constructed and tested. The oxygen transfer coefficient (k(L)a) and power requirements in the fermentor were determined with the water system under various conditions and the relationship between them in the fermentor was clarified. Also, the relationship between k(L)a and the apparent viscosity in the fermentor was investigated in the cell suspension system. The rotating drum fermentor was found to be superior to the mechanically agitated fermentor in the capacity of oxygen supply under high viscosity and low hydrodynamic stress conditions. This finding was also confirmed by the experiments with plant cell suspension cultures.     

Oxygen transfer and mixing in mechanically agitated airlift bioreactors

Gas holdup, mixing, liquid circulation and gas–liquid oxygen transfer were characterized in a large (∼1.5 m³) draft-tube airlift bioreactor agitated with Prochem^® hydrofoil impellers placed in the draft-tube. Measurements were made in water and in cellulose fiber slurries that resembled broths of mycelial microfungi. Use of mechanical agitation generally enhanced mixing performance and the oxygen transfer capability relative to when mechanical agitation was not used; however, the oxygen transfer efficiency was reduced by mechanical agitation. The overall volumetric gas–liquid mass transfer coefficient declined with the increasing concentration of the cellulose fiber solids; however, the mixing time in these strongly shear thinning slurries was independent of the solids contents (0–4% w/v). Surface aeration never contributed more than 12% to the total mass transfer in air–water.     

Immobilization and culture of coffee (Coffea arabica L.) cells on novel culture systems using a basket-shaped unit, “EGSTAR”

Summary A simple and new basket-shaped unit for agitation made of stainless steel (EGSTAR), in which immobilized coffee cells in Ca-alginate gel beads were packed, was placed in a jar fermentor (System-1). This system allowed the plant cells to grow submersed in the unit even at high agitation speed (650 rpm). Only a small amount of cells existed out of the EGSTAR. Most of the purine alkaloids produced were released into the medium. Suspended coffee cells in the jar fermentor were also possibly immobilized onto a polyurethane foam sheet fixed inside the net of the EGSTAR (System-2). The total cells in System-2 biotransformed theobromine to caffeine (77.9%). Other plant cell suspensions were also immobilized as efficiently as were the coffee cells in this system. Thus, System-2 is a simple and convenient system for immobilization of plant cells to produce secondary metabolites. This paper is Part 79 in the series of “Studies on Plant Tissue Cultures”. For Part 78, see Orihara, Y., Furuya, T., Hashimoto, N., Deguchi, Y., Tokoro, K., and Kanisawa, T., (1992)Phytochemistry 31: 827–831.     

Process-engineering characterization of small-scale bubble columns for microbial process development

Volumetric oxygen transfer rates and power inputs were estimated by a model of the formation of primary gas bubbles at the static sparger (sinter plate) of small-scale bubble columns and a common mass-transfer correlation for bubbles rising in a non-coalescent Newtonian electrolyte solution of low viscosity. Estimations were used to assess the dimensioning and possibilities of small-scale bubble column application with an height/diameter ratio of about 1. Estimations of volumetric oxygen transfer rates (<0.16 s^-1) and power inputs (<100 W m^-3) with a mean pore diameter of the static sparger of 13 µm were confirmed as function of the superficial air velocity (<0.6 cm s^-1) by measurements using an Escherichia coli fermentation medium. Small-scale bubble columns are thus to be classified between shaking flasks and stirred-tank reactors with respect to the oxygen transfer rate, but the maximum volumetric power input is more than one magnitude below the power input in shaking flasks, which is of the same order of magnitude as in stirred-tank reactors. A small-scale bubble columns system was developed for microbial process development, which is characterized by handling in analogy to shaking flasks, high oxygen transfer rates and simultaneous operation of up to 16 small-scale reactors with individual gas supply in an incubation chamber.     

Distributed parameter model of an airlift fermentor

A distributed parameter model for an airlift fermentor is presented. A riser represents the airlift fermentor, with plug flow in both gas and liquid phases, a well-mixed section that acts as gas separator, and a downcomer with plug flow. The set of equations proposed makes possible both the understanding and design of the system. Macroscopic balances shows a behavior that is very close to conventional continuous stirred tank fermentor from the viewpoint of biomass production. In addition, the model predicts concentration profiles of biomass, substrate and oxygen in the liquid, and oxygen in the gas phase. This allows estimation of optimal gas flow rate for sufficient oxygen transfer with minimum energy input.     

A continuous,multistage tower fermentor. I. Design and performance tests

The design of a continuous column fermentor with a multiple staging effect is described. The column is divided into four compartments by horizontal perforated plates and is provided with a central agitator shaft driving an impeller in each compartment. A tube at the center of each plate forms a liquid seal around the shaft and also acts as a “downcomer.” The fermentor is normally operated with counter-current flow of gas and medium. Fresh medium is added to the top stage and product is withdrawn from the bottom. The effect of plate and agitator design on fermentor performance was studied in terms of factor such as oxygen transfer rate, gas holdup, and interstage mixing. By proper choice of the design parameters, the fermentor was made to approximate a perfect four-stage cascade in terms of reactor performance. Preliminary experiments were performed with air-water systems, but a more realistic picture of fermentor performance was obtained in experience involving propagation of Escherichia coli. Data for business and substrate concentrations in each stage confirmed the staging effect of the apparatus. The fermentor operated in a stable manner for periods of more than two weeks.     

Design and oxygen-transfer potential of a pulsed continuous tubular fermentor

A new type of continuous fermentor has been developed which features an agitation-aeration system based on pulsed flow across perforated plates the use of plug flow to achieve a concentration gradient. The influence of the agitation-aeration parameters (in this case the pulsed speed) has been measured, and mathematical models have been produced for the gas hold-up, the power dissipated in agitation and aeration, the oxygen-transfer rate, and efficiency. The oxygen transfer is high, up to 600 mmol/liter hr with a transfer efficiency much higher than that published for any other technique.     

Reaction engineering studies of acetone-butanol-ethanol fermentation with Clostridium acetobutylicum

Acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum has been extensively studied in recent years because the organism is recognized as an excellent butanol producer. A parallel bioreactor system with 48 stirred-tank bioreactors on a 12 mL scale was evaluated for batch cultivations of the strictly anaerobic, butanol-producing C. acetobutylicum ATCC 824. Continuous gassing with nitrogen gas was applied to control anaerobic conditions. Process performances of ABE batch fermentations on a milliliter scale were identical to the liter-scale stirred-tank reactor if reaction conditions were identical on the different scales (e.g., initial medium, pH, temperature, specific evaporation rates, specific power input by the stirrers). The effects of varying initial ammonia concentrations (0.1-4.4 g L(-1) ) were studied in parallel with respect to glucose consumption and butanol production of C. acetobutylicum ATCC 824 as a first application example. The highest butanol yield of 33% (mol mol(-1) ) was observed at initial ammonia concentrations of 0.5 and 1.1 g L(-1) . This is the first report on the successful application of a 48 parallel stirred-tank bioreactor system for reaction engineering studies of strictly anaerobic microorganisms at the milliliter scale.     

Effects of paddle impeller geometry on power input and mass transfer in small-scale animal cell culture vessels

Process scaleup for stirred-tank animal cell cultures such as suspension and microcarrier cultures often begins at the bench scale in small spinner vessels. In order to initiate process development under the proper conditions, it is essential to know the physical conditions under which the cells are grown. In this article, power inputs and surface oxygen transfer rates to culture medium in 500-mL Corning spinner vessels were determined as a function of the impeller geometry, impeller height, and agitation speed. The results obtained indicate that power dissipation dependency differs from literature correlations and may compromise scale up at constant power input from these vessels. These results are of general utility to researchers using small-scale vessels.     

Effects of dissolved oxygen tension and agitation rate on the production of heat-shock protein glycoprotein 96 by MethA tumor cell suspension culture in stirred-tank bioreactors

Heat-shock protein glycoprotein (gp96) serves as a natural adjuvant for chaperoning antigenic peptide into the immune surveillance pathway. In our laboratory, MethA tumor cell suspension culture process has been recently developed for gp96 production in spinner flask. In this work, effects of dissolved oxygen tension (DOT) and agitation rate on this process were studied in stirred-tank bioreactor. The optimal conditions for gp96 production were different with those for MethA tumor cell growth. MethA tumor cell growth pattern was not much changed by various levels of DOT and agitation rate, while gp96 biosynthesis was more sensitive to DOT and agitation rate. Compared with 50% of DOT, the production and specific productivity of gp96 was increased by 27 and 66% at 10% of DOT, respectively. Compared with the agitation rate of 100 rpm, the production and volumetric productivity of gp96 was increased by 48 and 144% at the agitation rate of 200 rpm, respectively. Low DOT (i.e., 10% of air saturation) and high agitation rate (i.e., 200 rpm) were identified to be favorable for gp96 biosynthesis. The results of this work might be useful to scale-up the bioprocess into the pilot scale.     

Cost-effective dissolved oxygen monitor–controller for continuous culture

A number of devices for the control of the dissolved oxygen (DO) tension in small continuous cultures are now in use, but because of the sophisticated proportional control employed, are prohibitively expensive for many applications. This report describes a flexible cost-efficient DO monitor and controller which, including DO probe, valves, and gas solenoid, can be constructed for 400 dollars. The device employs two-position control of gas flow and agitation speed and is readily adaptable to a variety of application; Construction, operation, and performance in conjunction with a small fermentor are briefly discussed.     

The rotorfermentor. I. Description of the apparatus,power requirements,and mass transfer characteristics

A novel fermentation device, the rotorfermentor, is described and some experimental results are presented on power requirements and oxygen mass transfer characteristics of the rotorfermentor. This fermentation device is designed to achieve high cell concentrations in batch and continuous cultures. Basically, the rotorfermentor consists of a rotating microporous membrane which is enclosed within a stationary fermentor vessel. The metabolic products in the broth are continuously removed by filtration through the rotating microporous membrane while the growing cells can be retained inside the fermentor. This dual function of cell growth and concentration with the simultaneous removal of metabolic products is the essential characteristic of the rotorfermentor.     

Mechanical control of foaming in a bubble column

This study was performed to evaluate the effects of the air sparge rate, working liquid volume, liquid feed rate onto the disk, and disk diameter on the foam-breaking performance of foam-breaking apparatus with a rotating disk (FARD) installed in the bubble column. Experimental results showed that the smaller the air sparge rate and working liquid volume were, and the larger the liquid feed rate and disk diameter, the lower the critical disk rotational speed required for reduced foam-breaking. The presence of the effective ranges of the disk diameter and liquid feed rate for foam breaking was also confirmed. Furthermore, the quantitative predictions of the upper limits of the liquid feed rate, foam-breaking regions, and the required foam-breaking power were carried out, based on the results obtained above. Comparison of the FARD with two conventional mechanical foam-breaking spray-type apparati also demonstrated the highest level of the FARD in respect not only to foam-breaking performance but also to power requirements.     

An electromic controller for maintaining low dissolved oxygen levels in a bench-top fermentor

An electronic dissolved oxygen controller for use with a bench-top fermentor is described. It was designed to give an accurate control of low dissolved oxygen levels by continuous regulation of the agitation speed.     

Batch Production of Protein from Ethane and Ethane-Methane Mixtures

A culture of Graphium grows upon natural gas and a mineral salt solution. Ethane is the preferred substrate but methane is co-utilized. A stirred-tank type fermentor was used to study batch growth. Maximum production rate of biomass was 80 mg/liter.hr, at pH 4, using simple synthetic supporting medium with ammonium sulfate as a nitrogen source. This rate was observed after 40 hr of fermentation. A doubling time of 3.7 hr was observed. The corresponding specific growth rate was 0.187 per hr. A magnetic drive fermentor was used to study the effect of continuous recycle of gases in a gas-tight system. The rate of oxygen utilization is approximately 2.1 times higher than for ethane. Oxygen must not be allowed to become limiting in recycle gases. The calculated efficiency of overall biomass synthesis averages 30%. Hyphal and unicellular tissue of Graphium contains 52% protein. It compares favorably with standard FAO protein in its content of amino acids.     

Methods and milliliter scale devices for high-throughput bioprocess design

Based on electromagnetic simulations as well as on computational fluid dynamics simulations gas-inducing impellers and their magnetic inductive drive were optimized for stirred-tank reactors on a 10 ml-scale arranged in a bioreaction block with 48 bioreactors. High impeller speeds of up to 4,000 rpm were achieved at very small electrical power inputs (63 W with 48 bioreactors). The maxima of local energy dissipation in the reaction medium were estimated to be up to 50 W L⁻¹ at 2,800 rpm. Total power input and local energy dissipation are thus well comparable to standard stirred-tank bioreactors. A prototype fluorescence reader for 8 bioreactors with immobilized fluorometric sensor spots was applied for online measurement of dissolved oxygen concentration making use of the phase detection method. A self-optimizing scheduling software was developed for parallel control of 48 bioreactors with a liquid-handling system for automation of titration and sampling. It was shown on the examples of simple parallel batch cultivations of Escherichia coli with different media compositions that high cell densities of up to 16.5 g L⁻¹ dry cell mass can be achieved without pH-control within 5 h with a high parallel reproducibility (standard deviation<3.5%, n=48) due to the high oxygen transfer capability of the gas-inducing stirred-tank bioreactors.     

Determination of power consumption and volumetric oxygen transfer coefficient in bioreactors

A torque meter has been developed for determining the power consumption in a bench stirred tank. The device has been bonded in the stirrer shaft inside a commercial bench fermentor, in order to avoid frictional losses in the mechanical seal. Power consumption measurements in ungassed and gassed systems were obtained at different agitation and aeration conditions, for Newtonian and non-Newtonian fluids. Also, a "simple modified sulfite method" for volumetric oxygen transfer coefficient (k_La) determination was developed and the experimental data were correlated with the gassed power (P_g) by using well-known correlations presented in the literature.     

Bacterial cellulose production by Acetobacter xylinum in a 50-L internal-loop airlift reactor

Bacterial cellulose (BC) production was realized in a batch cultivation of Acetobacter xylinum subsp. sucrofermentans BPR2001 in a 50-L internal-loop airlift reactor. When the bacterium was cultivated with air supply, 3.8 g/L of BC was produced after 67 hours. When oxygen-enriched gas was supplied, the concentration of BC was doubled and the production rate of BC was 0.116 g/L. h, which was two times higher than that of air-supplied culture and comparable to that in a mechanically agitated stirred-tank fermentor. Bacterial cellulose produced by the airlift reactor formed a unique ellipse pellet (BC pellet), different from the fibrous form which was produced in an agitated stirred-tank fermentor. The BC-pellet suspension was demonstrated to have a higher volumetric oxygen transfer coefficient than the fibrous BC suspension in a 50-L internal-loop airlift reactor. The mixing time of BC-pellet suspension in the airlift reactor was also shorter than that in water.