Design and physical characteristics of a multistage,continuous tower fermentor

A multistage tower laboratory fermentor has been constructed consisting of eight compartments separated by sieve plates. Flow of substrate and air is concurrent from the bottom to the top of the column. It, was hoped that this system could be used to reproduce, simultaneously on a continuous basis, eight distinct phases of a batch growth curve. It was believed that the extent of batch curve simulation would depend upon the character of hydraulic mean residence time of broth in the column and in the individual compartments. The expected relationship did not occur. Rather it was found that growth in the column involved residence time characteristics not only for the fluid but also for the microorganisms, and for the growth limiting substrate. Depending upon the column operation, these could be distinct and different. The purpose of this investigation was to study the residence time distribution (RTD) of the continous (fluid) and dispersed (microorganisms) phases for model systems as well as for a yeast fermentation. Various degrees of flow nonideality, i.e., fluid blackflow and dispersed phase sedimentation, were noticed. The former seems to be due to interaction of the concurrent gas and liquid flow; it is particularly dependent upon void area of the sieve plate holes. Sedimentation is probably a function of plate design as well as cell size and density. It wa concluded that for a particular plate design the gas hold-up wass controlled by superficial air velocity and was the main parameter governing the differences between dispersed and continous phase(Rt1). This conclusion was supported by a computeraided styudy utilizing a mathematical model of fluid flow to fit the growth kinetics and cell distribution observed experimentally throughout the fermentor. Some advantages of foam control in the tower fermentor by surface active compounds are mentioned. Also, suggestions are made for carrying out fermentations that have two liquid phases, such as a hydrocarbon fermentation. The possibility of closely approximating plug-flow conditions in the multistage tower fermentor, a necessary condition for batch growth simulation, is discussed from a practical point of view.     

Repeated fed-batch lactic acid production in a packed bed-stirred fermentor system using a pH feedback feeding method

Lactic acid production by repeated fed-batch fermentation using free and immobilized cells of Lactobacillus lactis-11 in a packed bed-stirred fermentor (PBSF) system filled with different support materials including ceramic beads, macro-activated carbon cylinders and glass fiber balls was investigated. The results showed that the optimal support materials were the ceramic beads with diameters of 1–2 mm. Compared with the free cell fermentation system, lactic acid production and volumetric productivity in the PBSF system increased by 16.6 and 12.5%, respectively. Though the concentration of free cells decreased sharply, lactic acid production remained stable in five consecutive fed-batch runs using the PBSF system. pH gradients, immobilized cell concentration and mass diffusion in the packed bed were all affected by the recirculation rate of the culture broth. Maximum lactic acid production, productivity and yield occurred at a recirculation rate of 50 mL min⁻¹.     

A new sensor-the "filtration Probe"- for quantitative characterization of penicillin fermentation. III. An automatically operating probe

The filtration characteristics of the penicillin broth can be monitored semicontinuously using an automatic filtration probe. This probe operates aseptically and the broth samples (filtrate and filter cake) are recycled to the fermentor after each filtration. The collected data-filtrate volume and filter cake volume versus filtration time-can be related to the total biomass concentration in the fermentor.     

Ethanol fermentation of raw cassava starch with Rhizopus koji in a gas circulation type fermentor

Studies have been conducted in a gas circulation type fermentor in order to characterize the ethanol fermentation of uncooked cassava starch with Rhizopus koji. Results showed that ethanol concentration reached 13-14% (v/v) in 4-day broth, and the maximum productivity of ethanol was 2.3 g ethanol/L broth h. This productivity was about 50% compared to the productivity of a glucose-yeast system. Ethanol yield reached 83.5-72.3% of the theoretical yield for the cassava starch used. The fermentor used in the present work has been proven by experiment to be suitable for ethanol fermentation of the broth with solid substrate.     

Ethanol fermentation in a continuous tower fermentor

A mutant of Saccharomyces cerevisiae, which forms large, multicellular flocs in liquid culture, rapidly fermented media containing high concentrations of glucose (100-180 g/L) in a continuous nonaerated tower fermentor at 30 degrees C. The fermentor operated continuously for seven months. Batch and tower fermentor data were fitted to a kinetic model incorporating linear ethanol inhibition and Monod dependence on glucose. Conversion, ethanol yield, and ethanol productivity were related to the apparent fermentation time for initial glucose concentrations of 130 and 180 g/L. Productivities of 8-12 g ethanol/L h were achieved through the yeast bed giving conversions exceeding 90% of the theoretical yield.     

Performance of a two-stage fermentor with cell recycle for continuous production of lactic acid

The performasnce of a recycle two-stage fermentor with cell separators after each stage is analyzed numerically for continuous production of lactic acid. In this system, the bleed broth withdrawn from the first stage is provided to the second fermentor to reuse viable cells in the bleed. Biological rate expressions and parametric values are taken from the literature. The effects of operating parameters on the concentrations of total and viable cells, substrate and product in each stage, the lactic acid productivity and the substrate conversion are examined and discussed. With respect to overall productivity and conversion, it is found that the present fermentor system is more efficient than a conventional chemostat fermentor with cell recycle.     

A continuous,multistage tower fermentor. II. Analysis of reactor performance

A method for analyzing the reactor behavior of a continuous, multistage tower fermentor is described. A model consisting of a system of interconnected, ideal subreactors is set up on the basis of the fermentor's configuration and flow pattern. The residence time distribution curve is used to test the validity of the model and the relative quantities of flow streams and regions in the model are determined. A least-square fitting procedure between measured and calculated distribution curves is used to identify the proper model. The application of this method to real cultivation conditions is also discussed. Using this approach, the multistage tower fermentor is shown to be equivalent to a cascade of four perfectly mixed tanks with a backtracking stream between stages. The extent of backflow under various conditions has also been determined.     

Rapid sampling for analysis of in vivo kinetics using the BioScope: a system for continuous-pulse experiments

In this article we present a novel device, the BioScope, which allows elucidation of in vivo kinetics of microbial metabolism via perturbation experiments. The perturbations are carried out according to the continuous-flow method. The BioScope consists of oxygen permeable silicon tubing, connected to the fermentor, through which the broth flows at constant velocity. The tubing has a special geometry (serpentine channel) to ensure plug flow. After leaving the fermentor, the broth is mixed with a small flow of perturbing agent. This represents the start of the perturbation. The broth is sampled at different locations along the tubing, corresponding to different incubation times. The maximal incubation time is 69 s; the minimally possible time interval between the samples is 3-4 s. Compared to conventional approaches, in which the perturbation is carried out in the fermentor, the BioScope offers a number of advantages. (1) A large number of different perturbation experiments can be carried out on the same day, because the physiological state of the fermentor is not perturbed. (2) In vivo kinetics during fed-batch experiments and in large-scale reactors can be investigated. (3) All metabolites of interest can be measured using samples obtained in a single experiment, because the volume of the samples is unlimited. (4) The amount of perturbing agent spent is minimal, because only a small volume of broth is perturbed. (5) The system is completely automated. Several system properties, including plug-flow characteristics, mixing, oxygen and carbon dioxide transfer rates, the quenching time, and the reproducibility have been explored, with satisfactory results. Responses of several glycolytic intermediates in Saccharomyces cerevisiae to a glucose pulse, measured using a conventional approach are compared to results obtained with the BioScope. The agreement between the results demonstrates that the BioScope is indeed a promising device for studying in vivo kinetics.     

Changes in morphology of <Emphasis Type="Italic">Rhizopus chinensis</Emphasis> in submerged fermentation and their effect on production of mycelium-bound lipase

In order to control suitable mycelium morphology to obtain high lipase productivity by Rhizopus chinensis in submerged fermentation, the effects of fungal morphology on the lipase production by this strain both in shake flask and fermentor were investigated. Different inoculum level and shear stress were used to develop distinctive morphologies. Analyses and investigations both on micromorphology and macromorphology were performed. Study of micromorphology reveals that micromorphologies for dispersed mycelia and aggregated mycelia are different in cell shape, biosynthetic activity. Macromorphology and broth rheology study in fermentor indicate that pellet formation results in low broth viscosity. Under this condition, the oil can disperse sufficiently in broth which is very important for lipase production. These results indicate that morphology changes affected the lipase production significantly for R. chinensis and the aggregated mycelia were suggested to achieve high lipase production.     

Effect of interstage mixing in multistage culture systems on continuous biomass production

The significance of the interstage mixing on important process parameters of biomass production was studied. The experiments were performed in a multistage tower fermentor and in fermentors in series. The interstage mixing effect can be evaluated under conditions of geometrical similarity, identity of oxygen transfer rate, and identity of dilution rate per stage in the individual stages of both culture systems. Candida utilis was cultivated on a synthetic medium with ethanol as the sole carbon and energy source in the concentration range 10–100 g/liter. Dilution rate, temperature, and pH in each stage of both culture systems were kept constant. It was demonstrated that in the multistage tower fermentor the definite backflow which ensures the permanent reinoculation by adapted cells significantly decreases the inhibitory effect of higher ethanol concentrations on the cell growth and on the rate of ethanol utilization.     

A simple capillary viscosity meter for the on-line measurement and control of the biomass concentration in high-density cultures

A capillary viscosity meter was used for the on-line determination of the biomass concentration in a fermentation broth. At high cell densities the viscosity of the broth increases, which can be measured as the pressure drop over a capillary. Calibration aspects of this viscosity meter are presented, and the use of the device for the control of the biomass concentration in a membrane recycle fermentor is demonstrated.     

An experimental study of a modified turbidostat

Summary The efficacy of a modified turbidostat scheme for control of a continuous fermentor supporting substrate - inhibited growth of a methylotroph, L3, was experimentally examined. The control was based on continuous measure of optical density of fermentation broth. The experimental results illustrate the feasibility of the control scheme for effective startup as well as stabilization of a continuous fermentor under the influence of a load disturbance.     

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.     

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.     

发酵法生产鸟苷的生产性试验

以鸟苷生产菌Ｂａｃｉｌｌｕｓｓｕｂｉｔｉｌｉｓ２０６６为生产菌株,经摇瓶、２０Ｌ自控发酵罐、５００Ｌ发酵罐和２５０００Ｌ生产罐逐级放大试验,分别达到１５．６ｇ／Ｌ,１７．７ｇ／Ｌ,１３ｇ／Ｌ和１１ｇ／Ｌ的产量。     

Growth of E. coli in a stirred tank and in an air lift tower reactor with an outer loop

E. coli ATCC 11105 was cultivated in a 10-1 stirred tank reactor and in a 60-1 tower loop reactor in batch and continuous operation. By on-line measurements of O₂ and CO₂ concentrations in the outlet gas, pH, temperature, cell mass concentration X as well as dissolved O₂ concentration along the tower in the broth, gas holdup, broth recirculation rate through the loop and by offline measurements of substrate concentration DOC and cell mass concentration along the tower, the maximum specific growth rate _m , yield coefficients Y _X/S. Y _X/DOC and were evaluated in stirred tank and tower loop in batch and continuous cultures with and without motionless mixers in the tower and at different broth circulation rates through the loop. To control the accuracy of the measurements the C balance was calculated and 95% of the C content was covered.The biological parameters determined depend on the mode of operation as well as on the reactor used. Furthermore, they depend on the recirculation rate of the broth and built-ins in the tower. The unstructured cell and reactor models are unable to explain these differences. Obviously, structured cell and reactor models are needed. The cell mass concentration can be determined on line by NADH fluorescence in balanced growth, if the model parameters are determined under the same operational conditions in the same reactor.List of Symbols a, b empirical parameters in Eq. (1) - CPR kg/(m³ h) CO₂ production rate - C kg/m³ concentration - D l/h dilution rate - DOC kg/m³ dissolved organic carbon - I net. fluorescence intensity - K _S kg/m³ Monod constant - k _L a l/h volumetric mass transfer coefficient - OTR kg/(m³ h) oxygen transfer rate - OUR kg/(m³ h) oxygen utilization rate - RQ = CPR/OUR respiratory quotient - S kg/m³ substrate concentration - t h,min, s time - t _u min recirculation time - t _M min mixing time - v m³/h volumetric flow rate through the loop - X kg/m³ (dry) cell mass concentration - Y _X/S yield coefficient of cell mass with regard to the consumed substrate - Y _X/DOC yield coefficient of the cell mass with regard to the consumed DOC - Y _X/O yield coefficient of the cell mass with regard to the consumed oxygen - Z relative distance in the tower from the aerator with regard to the height of the aerated broth - l/h specific growth rate - _m l/h maximum specific growth rate Indices f feed - e outlet     

Computer modeling of antibiotic fermentation with on-line product removal

The fermentation of Streptomyces griseus for the production of cycloheximide is similar to other antibiotic fermentations in that product synthesis is subject to feedback regulation and the desired product is degraded in the fermentation broth. The productivity of this fermentation can thus be dramatically increased by removing the antibiotic from the whole broth as it is produced. One means for effecting this on-line product removal is to contact the whole fermentation broth with neutral polymeric resin immobilized in hydrogel beads. The antibiotic adsorbs to the immobilized resin via hydrophobic interactions. In this work, the adsorption of the antibiotic onto the immobilized resin was characterized. A biochemical model of the fermentation was then used to describe the time profiles of biomass, substrate, and antibiotic in a fermentation system in which whole broth is circulated from the fermentor through a continuously stirred extractor containing the adsorbent beads. Various operating conditions were examined to optimize the productivity of the fermentation.     

Critical evaluation of sampling techniques for residual glucose determination in carbon-limited chemostat culture of Saccharomyces cerevisiae

In this paper, three sampling techniques for rapid quenching of cellular metabolism and subsequent separation of cells from fermentation broth are compared: (i) quick freezing of fermentation broth directly in liquid nitrogen; (ii) quenching metabolism by exposing the fermentation broth to stainless steel beads (4-mm diameter) in a filter syringe precooled to -18 degrees C; and (iii) withdrawal of the filtrate through a 0.45 microm filter attached to a syringe and a needle inserted directly into the fermentor. It was concluded that use of liquid nitrogen as a quenching method to rapidly arrest cellular metabolism, for quantitative analysis of extracellular glucose, is not a very reliable method and that the filter syringe steel beads work very well.     

Stirred tank bioreactor with a recirculation loop for improved L-lysine production

Summary A bioreactor equipped with a recirculation loop was used to investigate the fermentation for L-lysine production. The broth was pumped from the bottom of the fermenter and fed back to the top. With the recirculation stream, antifoam was not required as the fermentation proceeded and the proposed system significantly improved the productivity for L-lysine fermentation.     

Measurement of dissolved carbon dioxide.

Several probes for measuring dissolved carbon dioxide (CO2) concentration were installed in a 68-litre fermentor and their effectiveness compared. Submerged silastic rubber tubing gave reproducible results over a wide range of operating conditions and was generally superior to all other probes evaluated. The silastic rubber probe was used to compare the partial pressure of CO2 in viscous fermentation media with that in the fermentor exhaust gas. No significant difference was found. Results show that determination of the CO2 partial pressure in the exhaust gas gives an excellent approximation of the partial pressure of dissolved CO2 in the liquid medium, eliminating the need for measurement of CO2 concentration in the broth.