Tower Fermenter Research Articles

Gravity-Driven Adaptive Evolution of an Industrial Brewer’s Yeast Strain towards a Snowflake Phenotype in a 3D-Printed Mini Tower Fermentor

We designed a mini tower fermentor that is suitable to perform adaptive laboratory evolution (ALE) with gravity imposed as selective pressure, and suitable to evolve a weak flocculating industrial brewers’ strain towards a strain with a more extended aggregation phenotype. This phenotype is of particular interest in the brewing industry, since it simplifies yeast removal at the end of the fermentation, and many industrial strains are still not sufficiently flocculent. The flow of particles (yeast cells and flocs) was simulated, and the theoretical retainment advantage of aggregating cells over single cells in the tower fermentor was demonstrated. A desktop stereolithography (SLA) printer was used to construct the mini reactor from transparent methacrylic acid esters resin. The printed structures were biocompatible for yeast growth, and could be sterilised by autoclaving. The flexibility of 3D printing allowed the design to be optimized quickly. During the ALE experiment, yeast flocs were observed within two weeks after the start of the continuous cultivation. The flocs showed a “snowflake” morphology, and were not the result of flocculin interactions, but probably the result of (a) mutation(s) in gene(s) that are involved in the mother/daughter separation process.

Ethanol production from date syrup with flocculent yeast: Optimization study

The current study was an attempt to produce ethanol from date syrup by using flocculent yeast, Saccharomyces uvarum. Due to its availability and cheap, the date syrup was used as the main carbon source. The central composite design (CCD) was applied to determine the optimum conditions of fermentation parameters in order to achieve high ethanol production. The selected parameters, fermentation temperature, concentration of date syrup sugar, and feed flow rate, were optimized through CCD. The study was conducted in a pilot scale plant tower fermenter. The highest conversion of the sugars was 95.75%, where it was achieved under the following optimum fermentation conditions: 29.06°C, sugar concentration of 55.00 mg/mL, and the feed flow rate of 100 mL/h (dilution rate 0.133 h−1). The flocculent yeast seemed to have a significant impact on the continuous ethanol production process due to its flocculent behavior. The phenomenon seemed to reduce the washout of cells with the product. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 818–823, 2013

Citric acid production: Surface culture versus submerged culture

Surface and submerged fermentation methods were used to produce citric acid byAspergillus niger using chemically defined media or cane molasses. Fermentation process parameters were optimized in pilot scale tower and tray fermenters. Fermentation was running from 10 - 20 days with pH controlled at 3 - 6.5. Citric acid concentrations varied from 60 - 100 g/L depending on the strain used, the substrate, the fermentation system and the general conditions under which fermentation took place (initial sugar concentration, aeration rate, inoculum size, pH and temperature). Some essential criteria such as lower process sensitivity to short interruptions or breakdowns in aeration, expenses for equipment, consumption of electrical energy and higher yield and productivity, showed that surface fermentation is superior to submerged fermentation. However, the yield and productivity obtained in submerged fermentation using indigenous strains of fungi is not yet high enough for commercial production. Key words: Citric acid, surface, submerged indigenous strains, yield, productivity.

Continuous Ethanol Production from Cassava Through Simultaneous Saccharification and Fermentation by Self-Flocculating Yeast Saccharomyces Cerevisiae CHFY0321

In this study, a fermentor consisting of four linked stirred towers that can be used for simultaneous saccharification and fermentation (SSF) and for the accumulation of cell mass was applied to the continuous production of ethanol using cassava as the starchy material. For the continuous process with SSF, the pretreated cassava liquor and saccharification enzyme at total sugar concentrations of 175 g/L and 195 g/L were continuously fed to the fermentor with dilution rates of 0.014, 0.021, 0.031, 0.042, and 0.05 h(-1). Considering the maximum saccharification time, the highest volumetric productivity and ethanol yield were observed at a dilution rate of 0.042 h(-1). At dilution rates in the range of 0.014 h(-1) to 0.042 h(-1), high production rates were observed, and the yeast in the first to fourth fermentor showed long-term stability for 2 months with good performance. Under the optimal culture conditions with a feed sugar concentration of 195 g/L and dilution rate of 0.042 h(-1), the ethanol volumetric productivity and ethanol yield were 3.58 g/L x h and 86.2%, respectively. The cell concentrations in the first to fourth stirred tower fermentors were 74.3, 71.5, 71.2, and 70.1 g dry cell/L, respectively. The self-flocculating yeast, Saccharomyces cerevisiae CHFY0321, developed by our group showed excellent fermentation results under continuous ethanol production.

Optimizing the culture conditions for higher inulinase production by Kluyveromyces sp. Y-85 and scaling-up fermentation

The response surface method (RSM) was used to optimize the medium for the production of inulinase by Kluyveromyces sp. Y-85. The inulinase production was adequately approximated with a full quadratic equation obtained from a four-factor-five-level central composite design. Analyses of the quadratic surfaces showed that in a 24-h fermentation at 30°C, the maximum inulinase activity 59.5 U/ml appeared at extract of Jerusalem artichoke, urea, beef extract, corn steep liquor concentrations 8.0%, 2.0%, 0.2% and 4.0%, respectively. We further investigated the fermentation in 15 l fermentor and scaling-up in 1000 l tower fermentor. The inulinase activity in the scaling-up was 68.9 U/ml, which was the highest production reported at present, indicating that Kluyveromyces sp. Y-85 was an excellent strain for industrial production.

Continuous Gas (CO2) Stripping to Remove Volatiles from an Alcoholic Beverage

Tower fermentors have been designed such that naturally evolved CO2 can be recirculated for continuous extraction of ethanol and other volatiles from beverage fermentation. Volatiles carried over i...

Ethanol fermentation in a tower fermenter using self-aggregatingSaccharomyces uvarum

A self-aggregating strain ofSaccharomyces uvarum (U4) was used as a biocatalyst to carry out continuous ethanol fermentation in a tower fermentor equipped with a cell separator. Cell aggregates (2–3 mm) formed a stable packed bed in the fermentor, and the cell separator retained yeast cells effectively. Corn steep liquor was used as a nitrogen source for the fermentation of corn syrup and black strap molasses. An ethanol productivity of 54 g/L/h was reached using corn syrup at a dilution rate of 0.7/h, and sugar concentration in the feed was 15% (w/v). For molasses fermentation, an ethanol productivity of 22 g/L/h was obtained at a dilution rate of 0.7/h, and sugar concentration in the feed was 12.5% (w/v). Ethanol yields obtained from tower fermentation are higher than those obtained from flask fermentation (96% for corn syrup fermentation and 92% for molasses fermentation). No significant loss in fermentation activity was observed after 3 mo of operation.

Relation between critical disk speed for foam-breaking of rotating-disk mechanical foam-breakers and foaming characteristics of solutions

For tower fermentors, i.e., bubble columns (BCs), treating various foaming liquids, the critical disk rotational speed N c required for foam-breaking of rotating-disk mechanical foam-breakers (MFRDs) fitted to BCs was studied in relation to the foaming characteristics of the liquids. An empirical equation was presented for predicting N c in foam-breaking regions. With this equation, it was found that prediction of N c of MFRDs fitted to BCs treating various liquids was possible regardless of the type of foaming liquid or its concentration.

Effect of sugar consumption on ethanol fermentation in a tower fermentor packed with self-aggregating yeast

A strain of self-aggregatingSaccharomyces uvarum was cultivated in a 6-L tower fermentor for continuous ethanol fermentation. Large aggregates (2–3 mm) were formed and packed in the column. The height of this packed region depends on the sugar concentration. As sugar concentrations were reduced to below a critical value, most of the large aggregates disintegrated into smaller aggregates (0.1–0.2 mm). Above the packed bed region, small aggregates and small amount of large aggregates were fluidized and formed a well mixed region by the liquid medium and the produced carbon dioxide. A mathematical model of a plug flow with consideration of axial dispersion and a Continuous Stirred Tank Reactor (CSTR) in series is proposed to describe such fermentor. The concentration profile of sugar can be simulated by this model. The height of the packed bed region can then be estimated based on the predetermined critical sugar concentration. Final ethanol concentration and the productivity of such fermentor can also be predicted.

Performance characteristics of a tower fermenter with mechanical foam control

AbstractFor a bubble column (BC) treating foaming liquids, the characteristics of a rotating‐disk mechanical foam‐breaker (MFRD) fitted to the BC were examined. The foaming behaviour of the BC and the foam‐breaking behaviour of the MFRD under various operating conditions were related to the changes in liquid hold‐up in the foam. The gas hold‐up in a mechanical foam‐control system (MFS) with the MFRD was confirmed to be greater than the gas hold‐up in a non‐foaming system (NS) including antifoam agent (AF). Comparison of the volumetric mass transfer coefficient between the MFS and the non‐foaming system, in terms of the specific power input, also demonstrated the superiority of mechanical foam control for oxygen transfer performance.

Design and operation of rotating‐disk foam‐breakers fitted to tower fermenters

AbstractThe design and operation of rotating‐disk mechanical foam‐breakers (MFRDs) fitted to tower fermenters, i.e. bubble columns (BCs), treating various foaming liquids were studied. The foam‐breaking behaviour of MFRDs fitted to BCs and the foaming behaviour of BCs were investigated respectively from the changes in the required critical disk rotational speed Nc and those in liquid hold‐up in the foam, øL. The effects of operating conditions on Nc and øL were evaluated quantitatively. On the basis of their results, the empirical equations for predicting Nc and øL in foam‐breaking regions, useful for the design and operation of MFRDs fitted to BCs, were obtained. The level of the required foam‐breaking power Pkc of MFRDs was also clarified in relation to the level of øL which reflects the foaming intensity of BCs and is related to the difficulty of foam‐breaking.

Modelling of concentration profiles in tower fermenter. The influence of the axial dispersion coefficient

The production of CO2 in tower fermenters which can cause back mixing, and thereby reducing the efficiency of such fermenters has been modelled with respect to fermentation. It is confirmed that the effect is significant. The effect of variations in the kinetic parameters, the maximum specific growth rate and the biomass yield coefficient was found to be insignificant. A good correlation between experimental and calculated data was obtained.

Ethanol production in an entrapped yeast cell column

The physical phenomena occurring in an entrapped cell tower fermenter have been studied and used to elucidate the kinetics of ethanol fermentation from A physical model is proposed, choosing the effectiveness factor as the main parameter for testing the reactor performance under different operating con An inhibition phenomenon following an increase in the inlet sugar concentration from 100 to 200 g 1 −1 was observed and has been ascribed to ethan

Prediction of bed height in a self-aggregating yeast ethanol tower fermenter

A packed bed region and a mixed region were observed in an ethanol tower fermenter packed with flocs of self-aggregating yeast. Sizes of yeast flocs were 2–3 mm and 0.2–0.3 mm in diameter in the packed bed region and the mixed region, respectively. Three major factors were found to affect the height of the packed bed region significantly. They were dilution rate, nutrient limitation, and hydrodynamic limitation. An empirical method was proposed using these three factors to predict the height of the packed bed region in the fermenter.

A multichamber tower fermentor for continuous ethanol fermentation with a self-aggregating yeast mutant

A multichamber tower fermentor, with a combined working volume of 30 L, was used to ferment sugar cane molasses to ethanol using a self-aggregating yeast mutant, Saccharomyces uvarum U4, derived from Saccharomyces uvarum ATCC 26602. The column was constructed of plexiglass tubing divided into four chambers of different depths by conical shaped dividers. Gas generated during fermentation was allowed to escape from each chamber of the column through a small tube at the top of the chamber. The rate of escape was controlled by manually-operated diaphragm valves. This design significantly reduced the turbulence caused by CO2 evolution and made it practical to maintain a total yeast bed depth double that previously sustained with this organism in long-term, single chamber tower fermentor tests. Using the multichamber tower fermentor, a 7–8% (w/v) ethanol-containing broth was continuously produced from molasses solution, with 160 g/L fermentable sugars, for more than 460 h of operation with a maximum dilution rate of 0.18 h-1. Less than 103 cells/mL in the effluent was observed during most of the operation.

Influence of feedstock source on biocatalyst stability and behavior, and on reactor performance, in continuous intensified ethanol fermentation

An ethanol process based on a gas-lift tower fermenter arrangement was used as a model system to show the strong dependence of reactor behavior on the developing chemical environment within the reactor. The reactor performance limits for realistic substrates—starch and molasses—are characterized and compared with those attainable on an ideal substrate, glucose.

Oxygen transfer during batch cultivation in an airlift tower fermentor

Oxygen transfer was studied in an airlift tower fermentor with motionless mixers (Kenics type). The intensity of oxygen transfer was characterized by its volumetric mass transfer coefficient, kLa, which was determined by the balance method. Experimental data of kLa were described by correlation equation and compared with results obtained for the airlift fermentor without motionless mixers with respect to energetic consumption. In addition, growth characteristics of the yeast culture Turulopsis ethanolitolerans cultivated on ethanol were also investigated.

Continuous production of ethanol from a glucose, xylose and arabinose mixture by a flocculent strain ofPichia stipitis

Enhanced rates of continuous ethanol production by a flocculent strain ofPichiastipitis from a sugar mixture (xylose 75%, glucose 20%, arabinose 5%) were attained using a single-stage gas lift tower fermentor. With a substrate feed of 50g/l, the biomass accumulated at a level near 50g/l, showed a maximum and stable ethanol productivity of 10.7 g/l.h, with a substrate conversion of 80%; the ethanol yield reached 0.41g/g. In these operating conditions, similar performances were obtained when D.xylose alone was supplied.

Liquid circulation and mixing in tower fermenters with recirculation loop

Liquid circulation and mixing time studies were carried out in a laboratory bubble column and modified bubble columns. Liquid circulation and mixing time are both strongly dependent on the geometrical configuration of the reactor. Internal recycle loop and external recycle loop shorten the mixing time compared to the bubble column.

Steady-state stability and dynamic behavior of continuous ethanol fermentation at high cell densities

A single stage gas-lift tower fermenter was used as a model system to study the steady-state stability and the dynamic behavior of an ethanol-inhibited continuous culture of Saccharomyces uvarum growing at high cell density. Empirical equations describing yeast growth and ethanol production rates in steady-state were combined with a mathematical description of the fermenter to predict steady-state stability and dynamic behavior when subjected to three sequential step changes in dilution rate from D = 2.13 to 0.213 h −1. Linearization and vector analysis of the theoretical model showed that eigen-values were real and negative, indicating that the system was stable and overdamped. When subjected to a step change in dilution rate, the experimental system responded immediately with a smooth overdamped transient to the next steady-state. Steady-state was reached within 6 h following a doubling in residence time. No cyclic or damped oscillations of glucose, ethanol or yeast concentration were observed in the theoretical or experimental system. The theoretical model predicted experimental behavior within 1.75 g l −1 root mean square deviation for large concentration ranges (glucose 210 → 16 g l −1; ethanol 16 → 88 g l −1) over experimental periods up to 28 h. The value of Y p/s = 0.425, calculated from steady-state experiments, gave the most precise prediction of dynamic behavior over the three transients. No evidence of significant metabolic or mass transfer lags was observed.