Effect of dilution rate on growth characteristics of Candida utilis in multistage culture systems with different interstage mixing

The effect of dilution rate on important process parameters of biomass production in two multistage culture systems with different interstage mixing has been examined. Experiments were performed in a multistage tower fermenter and in a cascade of fermenters. Measurements were made at steady-state of continuous culture under constant and identical values of ethanol concentration of 50 gl^?1 in the feed, temperature, OTR and pH in both culture systems used. The microorganism used was Candida utilis. Ethanol inhibition influenced cell growth rate due to the complete dissimilation of the restricted quantity of acetate to H₂O and CO₂, leading to insufficient energy generation. The value of ethanol concentration at which ethanol started to inhibit cell growth was a combined function of OTR, S_R and D. The presence of the interstage mixing resulted in more efficient ethanol conversion to biomass in the whole range of dilution rates and significantly lowered the risk of washing-out at high values of both S_R and D.     

Physiological characterictics and energy balance ofKlebsiella aerogenes in a multistage tower fermentor

Biomass growth, consumption of carbon and energy source, specific rates of formation of metabolic byproducts, biomass yield referred to the C-source and to oxygen, respiration rate and the value of RQ were studied in Klebsiella aerogenes CCM 2318 (on a synthetic glucose medium) at different specific growth rates. Maintenance coefficients and the total energy balance of the cultivation process were evaluated for a multistage tower fermentor with a defined interstage mixing. The results pointed to changes in both glucose metabolism and the physiological state of the population, brought about by changes in specific growth rate. As compared with a chemostat, the culture was found to exhibit a different physiological character is stages 1 and 4 despite a considerable interstage mixing.     

Effect of oxygen supply on growth ofKlebsiella aerogenes in a multistage tower fermentor

The effect of the rate of oxygen supply on biomass growth, consumption of carbon source formation of metabolic by-products, biomass yeilds referred to C-source and oxygen, respiration rate and the respiratory quotient was studied in a multistage tower fermentor with an interstage backflow, i.e. with a continuous reinoculation of the preceding stages. Experiments were done with Klebsiella aerogenes CCM 2318 in a synthetic glucose medium with constant glucose concentration in the feed, at pH 7.0. temperature 30 degrees C, and dilution rates 0.6 and 0.178 h-1 (referred to one stage). Different behavior of the culture was found at different dilution rates both with oxygen and under oxygen limitation. As compared with the chemostat system, the regime with an interstage backflow exhibited differences in respiration rate and CO2 formation; this attests to a considerably different physiological state of the cells.     

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.     

Effect of PO2 on growth and physiological characteristics of Candida utilis in a multistage tower fermentor

The effect of increasing the partial pressure of oxygen in the aeration gas on growth and physiological activity of the yeast Candida utilis in a multistage tower fermentor was studied. The measurements were made at steady states of continuous culture for single values of dilution rate, temperature, and pH in all stages of the fermentor and with one given ethanol concentration in the growth medium feed. The partial pressure of oxygen in the gas phase was changed in the range from 165 to 310 torr. The results revealed the existence of the upper critical value of the partial oxygen pressure in the gas phase. It was demonstrated that the upper critical value of PO ₂ influences not only the growth rate, biomass yield, and productivity but also the cell physiology resulting in changes of respiration activity and activity of alcohol and aldehyde dehydrogenases.     

Comparison of ethanol feed-type on yeast growth at various po2 levels

Summary The growth characteristics of the yeastCandida utilis in the individual stages of a multistage tower fermentor obtained with single- and multistream ethanol feeding were compared. In addition, various types of pure oxygen supply were tested for each type of ethanol feed. The results, obtained from steady-state continuous cultures, provided evidence that the two types of ethanol and oxygen supply significantly affect the cell growth rate, ethanol dissimilation rate, acetate excretion in the medium, biomass yield and productivity.     

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.     

Changes in steady state on introduction of a Lactobacillus contaminant to a continuous culture ethanol fermentation

Lactobacillus paracasei was introduced as a contaminant into a multistage continuous culture ethanol fermentation system at ratios of 1:100, 1:1, and 70:1 with Saccharomyces cerevisiae, but failed to overtake the yeast. None of the inoculation ratios allowed L. paracasei to affect S. cerevisiae in the first fermentor in the multistage system. S. cerevisiae remained constant at ∼3×10⁷ CFU/ml regardless of the bacterial inoculation level, and even at the 70:1 inoculation ratio, glucose, ethanol, and lactic acid concentrations did not change from the steady-state concentrations seen before bacterial inoculation. However, L. paracasei decreased steadily from its initial inoculation level of ∼2.2×10⁹ CFU/ml and stabilized at 3.7×10⁵ CFU/ml after 10 days of steady-state operation. Both organisms then persisted in the multistage system at an approximate L. paracasei/S. cerevisiae ratio of 1:100 which confirms that, in continuous fuel ethanol production, it would be difficult to eliminate this bacterium. Only when the pH was controlled at 6.0 in fermentor 1 (F1) were changes seen which would affect the multistage system. Ethanol concentration then decreased by 44% after 4 days of pH-controlled operation. This coincided with an increase in L. paracasei to >10¹⁰ CFU/ml, and a 4× increase in lactic acid concentration to 20 g/l. When the clarified contents from other fermentors (F2–F5) in the multistage system were used as growth media, L. paracasei was not able to grow in batch culture. This indicated that the first fermentor in the multistage system was the only fermentor capable of supporting the growth of L. paracasei under the described conditions. Journal of Industrial Microbiology & Biotechnology (2001) 27, 39–45. Received 26 February 2001/ Accepted in revised form 29 May 2001     

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.     

Rapid ethanol fermentations using vacuum and cell recycle

Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Cell recycle was employed in both atmospheric pressure and vacuum fermentations to achieve high cell densities and rapid ethanol fermentation rates. Studies were conducted with Saccharomyces cerevisiae (ATCC No. 4126) at a fermentation temperature of 35°C. Employing a 10% glucose feed, a cell density of 50 g dry wt/liter was obtained in atmospheric-cell recycle fermentations which produced a fermentor ethanol productivity of 29.0 g/liter-hr. The vacuum fermentor eliminated ethanol inhibition by boiling away ethanol from the fermenting beer as it was formed. This permitted the rapid and complete fermentation of concentrated sugar solutions. At a total pressure of 50 mmHg and using a 33.4% glucose feed, ethanol productivities of 82 and 40 g/liter-hr were achieved with the vacuum system with and without cell recycle, respectively. Fermentor ethanol productivities were thus increased as much as twelvefold over conventional continuous fermentations. In order to maintain a viable yeast culture in the vacuum fermentor, a bleed of fermented broth had to be continuously withdrawn to remove nonvolatile compounds. It was also necessary to sparge the vacuum fermentor with pure oxygen to satisfy the trace oxygen requirement of the fermenting yeast.     

Activated sludge process performance using a multistage tower aeration tank

This study's objective was to clarify both experimentally and theoretically whether a vertical multistage tower aeration tank system is advantageous as compared with a completely mixed system, particularly with respect to purification efficiency, sludge settleability, and excess sludge production. In comparing the two systems: (1) purification efficiency in the multistage tower aeration system with partial fluid mixing with a large Peclet number was higher than in a corresponding completely mixed system for all applied organic loadings; (2) the multistage tower aeration system had some definite advantages with respect to sludge settleability and excess sludge production; (3) the activated sludge system's higher performance with partial fluid mixing was shown quantitatively with the axial dispersion model in conjunction with growth kinetics which involved rapid uptake such as biosorption and subsequent oxidative biodegradation processes of organic substances. (c) 1993 John Wiley & Sons, Inc.     

Effect of multistream ethanol feeding on growth and physiological characteristics of Candida utilis in a multistage tower fermenter

The effect of using a multistream feed for carbon and energy supply on the growth and physiological activity of the yeast Candida utilis in a multistage tower fermenter has been studied. Measurements were made at steady states of continuous culture for single values of dilution rate, temperature and pH in all stages of the fermenter and with the same total ethanol supplied. A comparison of the results obtained with multistream and single-stream ethanol feeds revealed that the type of ethanol feed influences the cell growth rate, rate of ethanol dissimilation, biomass yield, productivity and the cell physiology in the individual stages of the fermenter. Multistream ethanol feeding eliminates the growth inhibition due to insufficient energy production from ethanol oxidation at higher partial pressure of oxygen in the aeration gas. Using the optimal type of ethanol feed, better process parameters for SCP production are achieved.     

A catalytic multistage fixed-bed tower bioreactor in an industrial-scale pilot plant for alcohol production

This article describes the development of an industrial-scale, multistage fixed-bed tower (MFBT) bioreactor using the promoter mineral kissiris for industrial alcohol production using free cells. Specifically, we examined the parameters needed to maintain operational stability from batch to batch for long periods. Pilot plant operations used one- and two-stage fixed-bed, 7000-L bioreactors. Likewise a 100,000-L, multistage fixed-bed tower system containing layered kissiris confirmed the laboratory results. Compared with a continuous stirred tank fermentor (CSTF) with recycle, a 30% reduction of energy demand and 10%-20% of the production costs are obtained. The latter are attributed to the increased ethanol concentration and alcohol productivity. (c) 1996 John Wiley & Sons, Inc.     

Design of a fast flow reactor for aerobic treatment of dilute waste streams

The design of a 125 liter aerated recirculating tower fermentor is presented. The tower has an external recirculation loop and a broth take-off point designed to give selective retention of biomass in the fermentor. This allows operation with high throughput rates using a low conentration feed. The aspect ratio in the main tower is approximately 14:1, but good mixing is promoted by the rapid recirculation of the broth. The construction of the fermentor and costs are given in details, illustrating that the fermentor may offer a cheap alternative to conventional systems.     

Continuous production of extracellular protease by Bacillus subtilis in a two-stage fermentor

Growth and protease production of Bacillus subtilis in semisynthetic and synthetic media were studied in batch culture and in a two-stage, laboratory scale, continuous fermentor. The amount, of extracellular protease production was measured under specific growth conditions in both stages of the ferment or. At the dilution rates employed, the cells in the first stage of the ferment or produced negligible quantities of protease, and the culture primarily functioned as a continuous inoculum for the second stage of the fermentor. The culture effluent from the second stage of the fermentor contained extracellular protease, on the average, equal to 60 per cent, of the activity that had been found in the supernatant of a 48-hr batch culture grown in a medium having the same composition as that in the continuous fermentor. Extracellular protease was produced in semisynthetic medium by B. subtilis in the two-stage fermentor for as long as 20 days without culture degeneration. Additional studies indicated that continuous protease production could also be achieved in a synthetic medium. The RNA/ protein ratios of cells grown in semisynthetic medium in batch culture and in each stage of the two-stage fermentor were examined. There was a positive correlation between the amount of protease produced by the cells and their RNA/ protein ratio. Techniques employed for continuous production of protease by B. subtilis and the potential use of the method for investigating the control of secondary metabolite synthesis are discussed.     

Ethanol production in multistage continuous, single stage continuous, Lactobacillus-contaminated continuous, and batch fermentations

Saccharomyces cerevisiae-based ethanol fermentations were conducted in batch culture, in a single stage continuous stirred tank reactor (CSTR), a multistage CSTR, and in a fermentor contaminated with Lactobacillus that corresponded to the first fermentor of the multistage CSTR system. Using a glucose concentration of 260 g l^–1 in the medium, the highest ethanol concentration reached was in batch (116gl^–1), followed by the multistage CSTR (106gl^–1), and the single stage CSTR continuous production system (60gl^–1). The highest ethanol productivity at this sugar concentration was achieved in the multistage CSTR system where a productivity of 12.7gl^–1h^–1 was seen. The other fermentation systems in comparison did not exceed an ethanol productivity of 3gl^–1h^–1. By performing a continuous ethanol fermentation in multiple stages (having a total equivalent working volume of the tested single stage), a 4-fold higher ethanol productivity was achieved as compared to either the single stage CSTR, or the batch fermentation.     

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.     

W135群脑膜炎球菌发酵工艺的研究

为研究A、C、Y、W 135群流脑多糖疫苗,针对W 135群脑膜炎球菌的生长特性,采用国产50L发酵罐,针对流脑半综合液体培养基中葡萄糖浓度;培养温度、菌种接种浓度、pH、通氧量及搅拌速度等因素对W 135群脑膜炎球菌生长的影响,选择最适的培养条件。结果表明,选择半综合培养基中补加1%的葡萄糖培养效果良好,菌种接种浓度直接影响多糖复合物产量;最适pH值6.5~7.5的范围可维持W 135群链球菌快速生长;温度控制在36.5±0.2℃可得到较高的培养产物;培养过程中加大通气量及搅拌速度对培养结果有明显改善。确立了W 135群脑膜炎球菌的最适培养条件,在确定培养条件后连续进行3批500L罐放大中试培养,达到规模化生产要求。     

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.     

Application of multistage continuous fermentation for production of fuel alcohol by very-high-gravity fermentation technology

A fermentation system to test the merging of very-high-gravity (VHG) and multistage continuous culture fermentation (MCCF) technologies was constructed and evaluated for fuel ethanol production. Simulated mashes ranging from 15% to 32% w/v glucose were fermented by Saccharomyces cerevisiae and the dilution rates were adjusted for each glucose concentration to provide an effluent containing less than 0.3% w/v glucose (greater than 99% consumption of glucose). The MCCF can be operated with glucose concentrations up to 32% w/v, which indicates that the system can successfully operate under VHG conditions. With 32% w/v glucose in the medium reservoir, a maximum of 16.73% v/v ethanol was produced in the MCCF. The introduction of VHG fermentation into continuous culture technology allows an improvement in ethanol productivity while producing ethanol continuously. In comparing the viability of yeast by methylene blue and plate count procedures, the results in this work indicate that the methylene blue procedure may overestimate the proportion of dead cells in the population. Ethanol productivity (Yps) increased from the first to the last fermentor in the sequence at all glucose concentrations used. This indicated that ethanol is more effectively produced in later fermentors in the MCCF, and that the notion of a constant Yps is not a valid assumption for use in mathematical modeling of MCCFs. Journal of Industrial Microbiology & Biotechnology (2001) 27, 87–93. Received 20 January 2001/ Accepted in revised form 28 April 2001