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.     

Induction effect of PO 2 during continuous yeast production from ethanol in a multistage tower fermentor

Summary The effect of the periodic variation of the partial pressure of oxygen in the aeration gas on biomass concentrations, ethanol conversion, yield and productivity during continuous cultivations of the yeast Candida utilis in a multistage tower fermentor was studied. The results were compared with those obtained under aeration conditions with a constant P_{O 2} in the aeration gas. The results demonstrated that, with the optimum P_{O 2} in the aeration gas, the aeration procedure with the periodic variation of P_{O 2} in the gas phase permitted achievement of the same process parameters as those under constant P_{O 2}. Using this new aeration procedure, the consumption of pure oxygen can be lowered by 55% to 60%. In addition, the significance of the induction effect of P_{O 2} on growth characteristics in the individual stages of the fermentor was proved.Symbols Ac Concentration of acetic acid (g/l) - i Number of stage - P_{O 2} Partial pressure of oxygen in the aeration gas (torr) - P_R Productivity of the fermentor (g cell dwt/l/h) - S_R Ethanol concentration in the feed (g/l) - S Ethanol concentration in the cultivation broth (g/l) - t Time of continuous cultivation (h) - X Cell dry weight concentration (g/l) - (Y_X/S)_W Yield of cell dry weight from ethanol for the whole fermentor (g cell dwt/g ethanol) - Concentration interval in which parameters varied during the long-term cultivation at constant constant P_{O 2}=263.5 torr in the aeration gas - ₁ Concentration interval in which parameters varied during the long-term cultivation before the increase of P_{O 2} in the aeration gas - ₂ Concentration interval in which parameters varied during the long-term cultivation immediately after the decrtease of P_{O 2} in the aeration gas - ₃ Concentration interval in which parameters varied during the long-term cultivation about 24 h after the decrease of P_{O 2} in the aeration gas - ₄ Concentration interval in which parameters varied during the long-term cultivation about 48 h after the decrease of P_{O 2} in the aeration gas     

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.     

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.     

Growth characteristics of Candida utilis on volatile substrate in a multistage tower fermentor.

The influence of increasing ethanol concentration in the feed on growth and physiological activity of the yeast Candida utlis was studied. The measurements were made at steady states of continuous culture under constant values of dilution rate, temperature, and pH in all stages of the fermentor; Synthetic ethanol was used as the sole source of carbon and energy in the concentration range 10-100 g/liter. The maximum biomass concentration in the effluent and maximum productivity was achieved at 75 g ethanol/liter in the feed. In respect to ethanol losses in the outlet and biomass yield, the optimum ethanol concentration in the input of the growth medium was found to be about 50 g/liter using a four-stage system.     

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.     

Performance of a perforated plate column as a multistage continuous fermentor

Microorganisms were continuously cultivated in multistage column consisting of ten perforated plate sections to which medium and air were supplied concurrently from the bottom. At steady state the cell concentration in the various stages was gradationally differentiated from the bottom to the top in the direction of medium flow. RNA content per unit cell concentration at each sage was determined. The cells in the lower stages were higher in RNA content than those from the upper stages. Wash out was observed to occur in the column at dilution rates which do not result in wash out in a single stage chemostat system. A study of the flow characteristics revealed that the overall performance of the plate column was equivalent to that of a multistage system, when hole diameter and hole area to column cross sectional area ratio were properly selected. This was true even in highly aerated conditions. These results indicated that the perforated plates in the column hindred intermixing through the plates, and that each stage functioned as an independent stirred vessel. Industrial and research application of this type fermentor was discussed.     

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.     

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.     

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.     

Oxygen transfer and mixing in a tower cycling fermentor

Tower cycling fermentors for the production of single-cell protein from volatile substrates were studied. The mass transfer, mixing and circulation patterns, and residence time distribution (RTD) curves were investigated in these vessels. This study suggests that the tower cycling fermentors for volatile substrates fermentation may improve product yields and at the same time reduce the power consumption, thereby resulting in a significant increase in operating cost savings and capital profits. The results of this research further indicate a future potential for commercial scale tower cycling fermentors.     

Automated fermentation equipment I. program-controlled fermentor

A fermentation system with a plug scheme unit has been developed, offering a variety of solutions to measurement, control, and operational problems. By means of the program unit, e.g., automatic pH control assigned to the dynamic of batch cultures and the feed of different ingredients controlled by a time program or a given variable have been solved. The continuous culture volume was controlled by a level controlled by a level controller equipped with a photosensor. A method was developed for variable control that provide information on the activity of the culture, and allows direct measurement of the different rate values, e.g., generation time or specific product formation rate. Applicability of the direct measurement of generation time is presented in the qualification of molasses and in a static off-line optimization process.     

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.     

In vitro simulation of rabbit cecal fermentation in a semi- continuous flow fermentor. I. Role of food substrate pretreatment]

A Rusitec semi-continuous flow fermentor was used to study the influence of enzyme pretreatment of food substrates on the fermentation profile over a 2-week period following inoculation with rabbit caecal contents. Three types of substrate were examined: 1) homogenized commercial rabbit feed; 2) the solid remains of this feed after digestion with alpha-amylase for 24 h; and 3) substrate 2 digested for 4 h with pepsin (double enzyme treatment). One of a pair of nylon pouches containing 15 g substrate was replaced each day, thus producing a uniform 48-h fermentation. Fermentation of the untreated feed (1) for 5-6 days produced a fermentation profile quite different from that obtained in vivo in the rabbit caecum: propionic acid accounted for over 35% of total volatile fatty acid (VFA), and butyric acid for about 15%. Amylase digestion (2) gave a stable ferment profile closer to the in vivo profile, except that propionic and butyric acids were similar at 15% of total VFA. Digestion with both amylase and pepsin (3) produced a stable fermentation profile very close to the in vivo profile: C2 > 60%, C3 < 11% and 17% < C4 < 21%. The rate at which membrane constituents (acid detergent fibre, ADF) were lost in 48 h was similar to the digestibility coefficient measured in vivo by others for the same basic feed. Lastly, there was a high percentage (about 5%) of volatile C5 fatty acids; this could be due to the discontinuous fermentor input of one pouch per 24 h. Thus, feed pretreated with both amylase and pepsin simulates, in vitro, rabbit caecal fermentation in a semi-continuous Rusitec type fermentor.     

A mathematical and empirical model of the performance of a membrane-coupled anaerobic fermentor

A mathematical model was developed to describe the performance of a membrane-coupled anaerobic fermentor (MCAF)-based process. In our experimental results, higher volatile fatty acid (VFA) recovery ratios were obtained at greater filtration ratios. The VFA recovery ratio peaked at an HRT of 12 h and a membrane filtration ratio of 0.95 at a constant SRT. Based on our simulation, the HRT and filtration ratio should be maintained at less than 1 day and above 0.9, respectively, to exceed an organic materials recovery ratio of 35% at a constant SRT of 10 days. Our empirical model, which predicts the effluent VFA concentration (C _o ), described the performance of the MCAF adequately. The model demonstrated that the outlet VFA concentration was a function of three independent parameters—HLR, input organic concentration (C _i ), and membrane filtration ratio (ϕ). Multiple regression analyses were conducted using 50 measurements of the MCAF, yielding the following relationship: C _o  = 0.278ϕ^1.13 C _i ^1.93 HLR^0.11. The correlation coefficient (R ²) was 0.90. The simulation results were consistent with the observed data; therefore, due to its simplicity, this model predicts the effluent VFA concentration of an MCAF adequately.     

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.     

Oxygen transfer modeling and simulations for an industrial continuous airlift fermentor

This article deals with the modeling of the oxygen transfer in an industrial airlift fermentor used for lactic yeast production on whey substrates. The purpose of this study was to improve the understanding of the interactions among the various parameters that govern the oxygen transfer phenomena in this type of fermentor. The reliability of the proposed model is demonstrated. The results of the investigations have been put into practice on the industrial scale and have contributed to monitor better the fermentation process. The model was also used to develop new ways of industrial fermentor design.     

A Mathematical model for ethanol production by extractive fermentation in a continuous stirred tank fermentor

Extractive fermentation is a technique that can be used to reduce the effect of end product inhibition through the use of a water-immiscible phase that removes fermentation products in situ. This has the beneficial effect of not only removing inhibitory products as they are formed (thus keeping reaction rates high) but also has the potential for reducing product recovery costs. We have chosen to examine the ethanol fermentation as a model system for end product inhibition and extractive fermentation and have developed a computer model predicting the productivity enhancement possible with this technique together with other key parameters such as extraction efficiency and residual glucose concentration. The model accommodates variable liquid flowrates entering and leaving the system, since it was found that the aqueous outlet flowrate could be up to 35% lower than the inlet flowrate during extractive fermentation of concentrated glucose feeds due to the continuous removal of ethanol from the fermentation broth by solvent extraction. The model predicts a total ethanol productivity of 82.6 g/L h if a glucose feed of 750 g/L is fermented with a solvent having a distribution coefficient of 0.5 at a solvent dilution rate of 5.0 h(-1). This is more than 10 times higher than for a conventional chemostat fermentation of a 250 g/L glucose feed. The model has furthermore illustrated the possible trade-offs that exist between obtaining a high extraction efficiency and a low residual glucose concentration.     

Behavior of Bacillus thuringiensis var. kurstaki under continuous phased cultivation in a cyclone fermentor

Summary Growth, sporulation, insecticidal crystalline protein (ICP) production and plasmids of Bacillus thuringiensis var. kurstaki (HD-1) were investigated during batch and continuous phased cultivation using a laboratory scale cyclone fermentor. When grown in batch culture at 28°C, 93% of the cells sporulated and produced ICP within 10 h of commencement of stationary phase. The batch culture runs were completed within 50 h of inoculation. A predominantly sporogenous and crystalliferous cell population was also obtained by second, stage processing of culture harvested from the first 10 to 25 cycles of continuous phased cultivation. In contrast, after 25 or more cycles of cultivation the population in the continuous phased culture shifted towards a predominantly asporogenous and acrystalliferous one. Culture conditions in continuous phased cultivation did not affect the plasmid content of B. thuringiensis (HD-1), yet influenced sporulation and plasmid-coded ICP production.