Average Ethanol Productivity Research Articles

Application of simultaneous saccharification and fermentation (SSF) from viscosity reducing of raw sweet potato for bioethanol production at laboratory, pilot and industrial scales

The aim of this work was to research a bioprocess for bioethanol production from raw sweet potato by Saccharomyces cerevisiae at laboratory, pilot and industrial scales. The fermentation mode, inoculum size and pressure from different gases were determined in laboratory. The maximum ethanol concentration, average ethanol productivity rate and yield of ethanol after fermentation in laboratory scale (128.51 g/L, 4.76 g/L/h and 91.4%) were satisfactory with small decrease at pilot scale (109.06 g/L, 4.89 g/L/h and 91.24%) and industrial scale (97.94 g/L, 4.19 g/L/h and 91.27%). When scaled up, the viscosity caused resistance to fermentation parameters, 1.56 AUG/g (sweet potato mash) of xylanase decreased the viscosity from approximately 30000 to 500 cp. Overall, sweet potato is a attractive feedstock for be bioethanol production from both the economic standpoints and environmentally friendly.

Fermentation of deproteinized cheese whey powder solutions to ethanol by engineered Saccharomyces cerevisiae: effect of supplementation with corn steep liquor and repeated-batch operation with biomass recycling by flocculation

The lactose in cheese whey is an interesting substrate for the production of bulk commodities such as bio-ethanol, due to the large amounts of whey surplus generated globally. In this work, we studied the performance of a recombinant Saccharomyces cerevisiae strain expressing the lactose permease and intracellular beta-galactosidase from Kluyveromyces lactis in fermentations of deproteinized concentrated cheese whey powder solutions. Supplementation with 10 g/l of corn steep liquor significantly enhanced whey fermentation, resulting in the production of 7.4% (v/v) ethanol from 150 g/l initial lactose in shake-flask fermentations, with a corresponding productivity of 1.2 g/l/h. The flocculation capacity of the yeast strain enabled stable operation of a repeated-batch process in a 5.5-l air-lift bioreactor, with simple biomass recycling by sedimentation of the yeast flocs. During five consecutive batches, the average ethanol productivity was 0.65 g/l/h and ethanol accumulated up to 8% (v/v) with lactose-to-ethanol conversion yields over 80% of theoretical. Yeast viability (>97%) and plasmid retention (>84%) remained high throughout the operation, demonstrating the stability and robustness of the strain. In addition, the easy and inexpensive recycle of the yeast biomass for repeated utilization makes this process economically attractive for industrial implementation.

Long-term repeated fed-batch ethanol fermentation in aerated condition

In this study, we attempted to assess the process stability of long-term fed-batch ethanol fermentation in the absence and presence of aeration (0.33 vvm). To examine the effect of aeration, a long-term repeated fed-batch operation was conducted for 396 h to mimic a long-term industrial bioethanol production process. In this long-term repeated fed-batch ethanol fermentation experiments, withdrawal-fill operation were conducted every 36 h for 10 repeat cycles. The whole operation was stably sustained in a quasi-steady state. The average maximal cell concentration and the average maximal ethanol production during operation were increased by 81.63 and 12.12%, respectively, when aeration was used. In addition, since aeration was carried out, the average ethanol yield slightly decreased by 4.03% and the average specific ethanol production rate decreased by 46.75% during operation. However, the average ethanol productivity increased by 17.53% when aeration was carried out. After 396 h of long-term repeated fed-batch ethanol fermentation, 1,908.9 g of ethanol was cumulatively produced when aeration was used, which was 12.47%, higher than when aeration was not used (1,697.2 g). Meanwhile, glycerol production was greatly decreased during long-term repeated fed-batch ethanol fermentation, in which the glycerol concentration in the culture broth decreased from about 34∼15 g/L. Thus, we can conclude that cell growth was greatly improved by overcoming ethanol inhibition and glycerol production was remarkably decreased when aeration was carried out, although aeration in ethanol fermentation decreased the specific ethanol production rate and ethanol yield.

Effect of controlled oxygen limitation on Candida shehatae physiology for ethanol production from xylose and glucose

Carbon distribution and kinetics of Candida shehatae were studied in fed-batch fermentation with xylose or glucose (separately) as the carbon source in mineral medium. The fermentations were carried out in two phases, an aerobic phase dedicated to growth followed by an oxygen limitation phase dedicated to ethanol production. Oxygen limitation was quantified with an average specific oxygen uptake rate (OUR) varying between 0.30 and 2.48 mmolO(2) g dry cell weight (DCW)(-1) h(-1), the maximum value before the aerobic shift. The relations among respiration, growth, ethanol production and polyol production were investigated. It appeared that ethanol was produced to provide energy, and polyols (arabitol, ribitol, glycerol and xylitol) were produced to reoxidize NADH from assimilatory reactions and from the co-factor imbalance of the two-first enzymatic steps of xylose uptake. Hence, to manage carbon flux to ethanol production, oxygen limitation was a major controlled parameter; an oxygen limitation corresponding to an average specific OUR of 1.19 mmolO(2) g DCW(-1) h(-1) allowed maximization of the ethanol yield over xylose (0.327 g g(-1)), the average productivity (2.2 g l(-1) h(-1)) and the ethanol final titer (48.81 g l(-1)). For glucose fermentation, the ethanol yield over glucose was the highest (0.411 g g(-1)) when the specific OUR was low, corresponding to an average specific OUR of 0.30 mmolO(2) g DCW(-1) h(-1), whereas the average ethanol productivity and ethanol final titer reached the maximum values of 1.81 g l(-1) h(-1) and 54.19 g l(-1) when the specific OUR was the highest.

Application of oscillation for efficiency improvement of continuous ethanol fermentation with Saccharomyces cerevisiae under very-high-gravity conditions

Compared with steady state, oscillation in continuous very-high-gravity ethanol fermentation with Saccharomyces cerevisiae improved process productivity, which was thus introduced for the fermentation system composed of a tank fermentor followed by four-stage packed tubular bioreactors. When the very-high-gravity medium containing 280 g l(-1) glucose was fed at the dilution rate of 0.04 h(-1), the average ethanol of 15.8% (v/v) and residual glucose of 1.5 g l(-1) were achieved under the oscillatory state, with an average ethanol productivity of 2.14 g h(-1) l(-1). By contrast, only 14.8% (v/v) ethanol was achieved under the steady state at the same dilution rate, and the residual glucose was as high as 17.1 g l(-1), with an ethanol productivity of 2.00 g h(-1) l(-1), indicating a 7% improvement under the oscillatory state. When the fermentation system was operated under the steady state at the dilution rate of 0.027 h(-1) to extend the average fermentation time to 88 h from 59 h, the ethanol concentration increased slightly to 15.4% (v/v) and residual glucose decreased to 7.3 g l(-1), correspondingly, but the ethanol productivity was decreased drastically to 1.43 g h(-1) l(-1), indicating a 48% improvement under the oscillatory state at the dilution rate of 0.04 h(-1).

Biological flocculation treatment on distillery wastewater and recirculation of wastewater

In the present study, a wastewater treatment system for the ethanol fermentation industry was developed by recycling distillery wastewater. The waste was able to be recycled for the next fermentation after being treated with bio-flocculation process. The bio-flocculation process contains three steps: screening, treatment with polyaspartic acid and filtration. When the filtrate from this process was recycled, the average ethanol production yield was very close to that in the conventional process using tap water. In contrast, the recycle of wastewater without flocculation and with chemical flocculation showed negative effects on ethanol yield as recycling was repeated. This new process was confirmed to have stable operation over ten recycles. Hazardous materials influencing distillery wastewater recycles on fermentation were also considered. It was found that the content of suspended solids (SS), volatile acid and Fe ions inhibited fermentation and resulted in a decreased ethanol yield. Bio-flocculation was shown to be an effective way to diminish the content of inhibitory compounds drastically when the waste was recirculated.

An innovative consecutive batch fermentation process for very high gravity ethanol fermentation with self-flocculating yeast

An innovative consecutive batch fermentation process was developed for very high gravity (VHG) ethanol fermentation with the self-flocculating yeast under high biomass concentration conditions. On the one hand, the high biomass concentration significantly shortened the time required to complete the VHG fermentation and the duration of yeast cells suffering from strong ethanol inhibition, preventing them from losing viability and making them suitable for being repeatedly used in the process. On the other hand, the separation of yeast cells from the fermentation broth by sedimentation instead of centrifugation, making the process economically more competitive. The VHG medium composed of 255 g L(-1) glucose and 6.75 g L(-1) each of yeast extract and peptone was fed into the fermentation system for nine consecutive batch fermentations, which were completed within 8-14 h with an average ethanol concentration of 15% (v/v) and ethanol yield of 0.464, 90.8% of its theoretical value of 0.511. The average ethanol productivity that was calculated with the inclusion of the downstream time for the yeast flocs to settle from the fermentation broth and the supernatant to be removed from the fermentation system was 8.2 g L(-1) h(-1), much higher than those previously reported for VHG ethanol fermentation and regular ethanol fermentation with ethanol concentration around 12% (v/v) as well.

On-line estimation of sugar concentration for control of fed-batch fermentation of lignocellulosic hydrolyzates by Saccharomyces cerevisiae.

A feed control strategy, based on estimated sugar concentrations, was developed with the purpose of avoiding severe inhibition of the yeast Saccharomyces cerevisiae during fermentation of spruce hydrolyzate. The sum of the fermentable hexose sugars, glucose and mannose, was estimated from on-line measurements of carbon dioxide evolution rate and biomass concentration by use of a simple stoichiometric model. The feed rate of the hydrolyzate was controlled to maintain constant sugar concentration during fed-batch fermentation, and the effect of different set-point concentrations was investigated using both untreated and detoxified hydrolyzates. The fed-batch cultivations were evaluated with respect to cellular physiology in terms of the specific ethanol productivities, ethanol yields, and viability of the yeast. The simple stoichiometric model used resulted in a good agreement between estimated sugar concentrations and off-line determinations of sugar concentrations. Furthermore, the control strategy used made it possible to maintain a constant sugar concentration without major oscillations in the feed rate or the sugar concentration. For untreated hydrolyzates the average ethanol productivity could be increased by more than 130% compared to batch fermentation. The average ethanol productivity was increased from 0.12 to 0.28 g/g h. The productivity also increased for detoxified hydrolyzates, where an increase of 16% was found (from 0.50 to 0.58 g/g h).

Abscisic acid and hypoxic induction of anoxia tolerance in roots of lettuce seedlings.

Lettuce (Lactuca sativa L.) seedlings were subjected to anoxic stress after ABA-pretreatment (ABA-PT) or hypoxic-pretreatment (H-PT). The H-PT increased the survivability of the anoxia in roots of the seedlings by 5.2-fold compared to that of non-pretreated (N-PT) seedlings. ABA-PT also increased the survivability at concentrations greater than 1 microM, and the survivability increased with increasing ABA doses. At 100 microM ABA, the survivability was 4.5-fold greater than that of N-PT seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots became 3.1- and 3.4-fold greater than that of N-PT seedlings following 100 microM ABA-PT and H-PT seedlings, respectively. After the onset of anoxic stress, ADH activities in all roots increased, but the activities in H-PT and ABA-PT roots remained much greater than that in N-PT roots, and the average ethanol production rate for the initial 6 h was 5.3, 4.0 and 1.4 micromol g(-1) FW h(-1) for H-PT, ABA-PT and N-PT roots, respectively. Roots of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the ABA-PT and H-PT seedlings than in the N-PT seedlings. These results suggest that the ABA-PT and H-PT may maintain ATP levels due to activation of ethanolic fermentation, which may be one of the causes of the increasing anoxia tolerance in the seedling roots. Measurement of endogenous ABA levels, however, showed that ABA levels did not increase during the H-PT, suggesting that the H-PT does not increase tolerance through an increase in ABA levels.

5607623 Inhibition of carbon dioxide corrosion of metals: Benton William J; Koskan Larry Magnolia, TX, United States assigned to Donlar Corporation

A zero-discharge system for the alcohol fermentation industry was developed by recycling distillery waste (stillage). Stillage was able to be recycled as cooking water for the next fermentation after treating it with appropriate separation processes. Ultrafiltration with a ceramic membrane played a key role in the separation processes. When the permeate from the ultrafiltration of stillage was recycled to the cooking step, the total fermentation time was prolonged from 60 to 70–80 h, but the average ethanol production yield (8.8%) was similar to that in the conventional process (9.0%). In contrast, direct recycle of stillage without membrane filtration showed negative effects on both fermentation time and alcohol yield as recycling was repeated. This new process was confirmed to have stable operation over eight recycles. This new clean technology for the ethanol production industry makes it possible to eliminate the stillage treatment steps using the conventional biological treatment processes such as anaerobic digestion and activated sludge steps currently being operated in industry.

Development of clean technology in alcohol fermentation industry

A zero-discharge system for the alcohol fermentation industry was developed by recycling distillery waste (stillage). Stillage was able to be recycled as cooking water for the next fermentation after treating it with appropriate separation processes. Ultrafiltration with a ceramic membrane played a key role in the separation processes. When the permeate from the ultrafiltration of stillage was recycled to the cooking step, the total fermentation time was prolonged from 60 to 70–80 h, but the average ethanol production yield (8.8%) was similar to that in the conventional process (9.0%). In contrast, direct recycle of stillage without membrane filtration showed negative effects on both fermentation time and alcohol yield as recycling was repeated. This new process was confirmed to have stable operation over eight recycles. This new clean technology for the ethanol production industry makes it possible to eliminate the stillage treatment steps using the conventional biological treatment processes such as anaerobic digestion and activated sludge steps currently being operated in industry.

Continuous ethanol production from nonsterilized carob pod extract by immobilizedSaccharomyces cerevisiae on mineral kissiris using a two-reactor system

The continuous production of ethanol from nonsterilized carob pod extract by immobilized Saccharomyces cerevisiae on mineral kissiris using one- and two-reactor systems has been investigated. A maximum ethanol productivity of 9.6 g/L/h was obtained at an initial sugar concentration of 200 g/L and D = 0.4 h-1 with 68% of theoretical yield and 34% of sugar utilization using the one-reactor system. At S0 = 200 g/L, D = 0.05 h-1, 83% of theoretical yield, and 64% of sugar utilization, an ethanol productivity of 2.6 g/L/h was achieved. In the two-reactor system, a maximum ethanol productivity of 11.4 g/L/h was obtained at S0 = 200 g/L and D = 0.4 h-1 with 68.5% of theoretical yield and 41.5% of sugar utilization. The two-reactor system was operated at a constant dilution rate of 0.3 h-1 for 60 d without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical), and sugar utilization were 10.7 g/L/h, 71.5%, and 48%, respectively.

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed‐bed reactor

AbstractThe continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed‐bed reactor has been investigated. At a substrate concentration of 150 g dm−3, maximum ethanol productivity of 16 g dm−3 h−1 was obtained at D = 0·4 h−1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h−1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm−3. Maximum ethanol productivity of 24·5 g dm−3 h−1 was obtained at D = 0·5 h−1 with 58·8% of theoretical yield and 85% sugars′ utilization when non‐sterilized carob pod extract containing 200 g dm−3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h−1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm−3 h−1, 58·8% and 85·5%, respectively.

Continuous ethanol fermentation using immobilized yeast in a fluidized bed reactor

AbstractContinuous ethanol fermentation of glucose using fluidized bed technology was studied. Saccharomyces cerevisiae were immobilized and retained on porous microcarriers. Over two‐thirds of the total reactor yeast cell mass was immobilized. Ethanol productivity was examined as dilution rate was varied, keeping all other experimental parameters constant.Ethanol yield remained high at an average of 0.36 g ethanol g−1 glucose (71% of theoretical yield) as the dilution rate was increased stepwise from 0.04 h−1 to 0.14 h−1. At a dilution rate of 0.15 h−1, the ethanol yield steeply declined to 0.22 g ethanol g−1 glucose (44% of theoretical yield). The low maximum percentage of theoretical yield is primarily due to an extended mean cell residence time, and possibly due to the inhibitory effect of a high dissolved carbon dioxide concentration, enhanced by the probable intermittent levels of low pH in the reactor.Constant ethanol production was possible at a high glucose loading rate of 840 g dm−3 day−1 (attained at a dilution rate of 0.14 h−1). Although the highest average ethanol concentration (97.14 g dm−3) occurred at the initial dilution rate of 0.04 h−1, the peak average ethanol production rate (2.87 g (g yeast)−1 day−1) was reached at a greater dilution rate of 0.11 h‐1. Thus, the optimal dilution rate was determined to be between 0.11 h−1 and 0.14 h−1.Ethanol inhibition on yeast cells was absent in the reactor at average bulk‐liquid ethanol concentrations as high as 97.14 g dm−3. In addition, zero‐order kinetics on ethanol production and glucose utilization was evident.

Immobilization of Saccharomyces cerevisiae on γ-alumina pellets and its ethanol production in glucose and raisin extract fermentation

The immobilization of Saccharomyces cerevisiae cells on γ-alumina pellets was examined by electron microscope and by measurement of the electrokinetic charge of the cells and the γ-alumina pellets. Repeated batch fermentations (about 20) were done for glucose and raisin extract, separately, with an average ethanol production of 80 g/ l·d and 52 g/ l·d respectively.

Repeated batch conversion of raw starch to ethanol using amylase immobilized on a reversible soluble-autoprecipitating carrier and flocculating yeast cells.

A raw-starch-digesting amylase, Dabiase K-27, was immobilized covalently on an enteric coating polymer (hydroxypropyl methylcellulose acetate succinate: AS) as a carrier which is autoprecipitating in an insoluble state below pH 4 as well as reversibly soluble-insoluble depending on pH. Dabiase immobilized on AS (D-AS) showed a sharp response of solubility to slight changes of pH without decrease in enzymatic activity. Moreover, D-AS in an insoluble state had good properties of sedimentation and a large portion of D-AS spontaneously precipitated after 10 min at pH 4. D-AS was used successively for repeated ethanol production from raw starch, in which D-AS and flocculating yeast cells were separated simultaneously from a product solution by sedimentation in a reactor with a conical bottom. In the five batches of 10% raw starch, the total amount of ethanol produced from 150 g of raw starch was 61 g, a value of which corresponds to the average ethanol productivity of 0.85 g/l/hr. The repeated ethanol production by a combination of D-AS and flocculating yeast cells is a promising procedure for effectively using the enzyme and recovering the product solution economically in a heterogeneous culture system containing a solid substrate.

Film fermentor for ethanol production by yeast immobilized on cotton cloth

Saccharomyces cerevisiae cells were immobilized on cotton cloth. The resulting yeast films were placed in parallel in a rectangular fermentor which was designed for scale-up. Ethanol production from sugars in the hydrolysate of Jerusalem artichoke tubers was studied in three modes of operation: batch, circulated batch and continuous flow. Circulated batch fermentation gave the shortest time of fermentation and accordingly the highest average ethanol productivity.