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.     

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.     

Xylanase mass transfer studies in aqueous two-phase systems using spray and sieve plate columns

Aqueous two-phase systems (ATPSs) have long been used for biomolecule partitioning; these systems offer the possibility of using continuous or semicontinuous extraction processes. They require relatively simple equipment like spray or sieve plate columns that can be adapted for use in ATPSs. The aim of this work was to study the semicontinuous extraction of a model enzyme, xylanase, in spray and sieve plate columns, since, unlike centrifugal contactors, the cost of construction and maintenance of this equipment is low and it is easy to operate. For the spray column, the dispersed phase hold-up and overall mass transfer coefficients K(D) a were evaluated for different column heights and for different superficial velocities of the dispersed phase (light phase). Results indicated that an increase in superficial velocity in the range of 0-0.18 mm/s of the dispersed phase had a positive effect on K(D) a and on hold-up in all column heights studied, 75, 161 and 246 mm. For the same superficial velocity of the dispersed phase, the larger the hold-up was, the shorter the column. For the sieve plate column, the effects of the superficial velocity of the dispersed phase and the number of plates were also studied. Results showed that the K(D) a and hold-up increased with an increase in both parameters. The selectivity of separation of xylanase and BSA (model contaminant) was very high, since 60% of the enzyme was extracted in the light phase, whereas no significant amount of BSA was extracted. The possibility of using the sieve plate column in continuous operation for enzyme extraction was studied because previous work had only addressed the semicontinuous extraction of enzyme. The residence time distribution of the PEG phase using different superficial velocities of the salt phase was studied in continuous operation. The time required to reach the steady state was 40 min, and 70% of the xylanase was recovered. It was found that the Modified Power Spline software was well adjusted to the experimental results.     

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.     

Computation of the fraction of induced cells in enzyme induction systems

A theoretical model is developed for continuous multistage enzyme production systems, which consist of a growth fermentor used for growing microorganisms rapidly without enzyme production and a subsequent system of induction reactors in which enzymes induction and production occurs. The model allows the computation of the fraction of induced cells residing in the induction reactor for organisms exhibiting a lag phase in enzyme induction. For this model a general analytical solution was obtained for the cumulative internal residence time distribution of a series of n well-stirred vessels with a recycle. The theoretical results are compared in a preliminary way with experimentally measured cellulase productivities of continuous multistage cellulose fermentations with Trichoderma viride QM 9414.     

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.     

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 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.     

Fermentors with the power introduced by aerating gas

In the present work methods and results of investigations on optimal construction of fermentor elements by multifactor planning at a random number of levels of any factor are presented. The optimal design of column fermentor of 0.02–100 m³ volume with sieve plates containing downcomers and with power introduced by aerating gas has been worked out. Several alternative designs have been compared by examining mass transfer rates, power requirements, and other operating characteristics. Several fermentor designs with the power introduced by aerating gas are discussed with respect to their performance for cultivating various microorganisms (yeast and bacteria).     

The tubular loop batch fermentor: Basic concepts

A tubular loop batch fermentor has been designed and constructed, and was found to behave in a similar manner to a conventional stirred tank reactor. It appeared that foaming could be greatly reduced as no air ever encountered the impeller. The fluid mechanics of pipe flow are considerably simpler than tank flow patterns. On this basis a design procedure for a large scale tubular fermentor was outlined, which had considerable advantages over the more complex scale-up problems of a tank fermentor.     

Pressure drop,gas hold-up,and oxygen transfer in tower systems

Pressure drop, gas hold-up, and oxygen transfer were investigated in a sieve tray column, a column with Koch motionless mixers, and a bubble column. The oxygen transfer experiments were conducted using cocurrent flow of gas and liquid under steady-state conditions with oxygen transfer from the gas to the liquid phase. The oxygen transfer rates and efficiencies of the sieve tray column and the column with Koch mixers were found to be superior to those of the conventional bubble column. Gas hold-up was also greater when sieve trays or Koch mixers were inserted in the tower. The pressure drop was found to be primarily due to the liquid head in all three columns.     

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.     

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.     

Apparent and true longitudinal concentration profiles in reciprocating plate column

Mass transfer for kerosene-water system with benzoic acid and n-butyric acid as solutes has been studied in a reciprocating plate column at different operating conditions including the agitation rate of the plate stack, the plate geometry, the flow rates of the phases and the direction of mass transfer. Apparent and true concentration profiles for the dispersed and the continuous phase along the length of the column were generated, taking axial mixing of the phase into consideration. It is noticed that high agitation rate for the plate stack and low free area for the plate give rise to large difference between the apparent and true values. These observations also agree with the data obtained for carbon dioxide — water system studied in a reciprocating plate column.     

Some aspects of hydrodynamics in multistage bubble columns

Hydrodynamic aspects covering the flow regimes and dispersed phase holdup have been investigated in multistage bubble columns using different geometries for the horizontal perforated plates. Air-water, air-kerosene and air-CMC solutions are investigated to cover a wide range in physical properties of liquids. The data show that the plate perforation diameter, plate spacing and the gas flow rate are the principal variables influencing the flow regimes and the dispersed phase holdup.     

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.     

Reactors for continuous primary beer fermentation using immobilised yeast

A continuous multistage column bioreactor with fluidised beds and continuous gas-lift bioreactor system with immobilised yeast Saccharomyces cerevisiae was developed for the first step of wort fermentation. The system of gas-lift reactor with yeast entrapped in calcium pectate beads was stable for 5 weeks by the optimal residence time of 12.75h and produced beer with a composition and flavour profile similar to that of beer produced by batch fermentation. Concentration of diacetyl was less than 0.1mg/l.     

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.     

Continuous fermentation in slant tubes

Continuous, steady-state grape-juice fermentation, carried out in experimental slant-tube fermentors, was characterized by complete fermentation, even at fast pumping rates, because efficient cell retention, as well as rapid yeast growth, quickly built cell density up to the limit permitted by the juice supply rate. Essentially complete fermentation was easily achieved with a juice residence time of 3.1 hr, compared to about 120 hr in normal batch fermentation. Successful continuous fermentation required constancy of gas and liquid flow through the tubes, placing some restrictions on choice of tube configurations. The validity of design equations, developed previously from a settling model, was tested, and some practical aspects of their application to fermentor design and operation were demonstrated.     

FLAVOR MODIFICATION OF MILK CHOCOLATE BY CONCHING IN A TWIN-SCREW, CO-ROTATING, CONTINUOUS MIXER

Short-time continuous conching of chocolate offers significant economic advantages over traditional long-time batch methods. High-shear continous mixers can affect conching in a matter of minutes as compared to hours for traditional systems. Milk chocolate conched in two twin-screw, co-rotating, continous mixers operating in series was compared by a variety of sensory methods to chocolate conched by a batch method. A significant difference (P < 0.05) in flavor was found between chocolates conched at 60C by the continuous and batch methods, yet there was no preference for either chocolate. Chocolate conched by the batch method (23 h at 60C) had stronger caramel flavor (P < .10) than chocolate conched continuously, but there were no significant differences (P < .10) in sweet, chocolate or milk flavor. In the continuous system, caramel flavor generally increased with conching temperature and residence time; although, at the highest temperature (95C) and the longest residence time (7.5 min) caramel flavor decreased. Increasing the temperature of continuous conching from 70 to 90C produced chocolate significantly (P < .10) more like chocolate conched in a batch system for 21.5 h at 60C.