Continuous Ethanol Fermentation Research Articles

Global Stabilizing Control of a Continuous Ethanol Fermentation Process Starting from Batch Mode Production

Global Stabilizing Control of a Continuous Ethanol Fermentation Process Starting from Batch Mode Production

Saccharomyces cerevisiae employs complex regulation strategies to tolerate low pH stress during ethanol production

BackgroundIndustrial bioethanol production may involve a low pH environment caused by inorganic acids, improving the tolerance of Saccharomyces cerevisiae to a low pH environment is of industrial importance to increase ethanol yield, control bacterial contamination, and reduce production cost. In our previous study, acid tolerance of a diploid industrial Saccharomyces cerevisiae strain KF-7 was chronically acclimatized by continuous ethanol fermentation under gradually increasing low-pH stress conditions. Two haploid strains B3 and C3 having excellent low pH tolerance were derived through the sporulation of an isolated mutant. Diploid strain BC3 was obtained by mating these two haploids. In this study, B3, C3, BC3, and the original strain KF-7 were subjected to comparison transcriptome analysis to investigate the molecular mechanism of the enhanced phenotype.ResultThe comparison transcriptome analysis results suggested that the upregulated vitamin B1 and B6 biosynthesis contributed to the low pH tolerance. Amino acid metabolism, DNA repairment, and general stress response might also alleviate low pH stress.ConclusionSaccharomyces cerevisiae seems to employ complex regulation strategies to tolerate low pH during ethanol production. The findings provide guides for the construction of low pH-tolerant industrial strains that can be used in industrial fermentation processes.

Robust nonlinear model predictive control of cascade of fermenters with recycle for efficient bioethanol production

In this paper, dynamical behavior and control of the continuous ethanol fermentation process are studied. The process productivity is improved by using two fermenters connected in series with recycle of cells. First, dynamical behavior and productivity of the cascade system are studied by using numerical bifurcation analysis. Then, multi-stage nonlinear model predictive control (MS-NMPC), classical and offset-free NMPCs algorithms are designed to eliminate the undesired oscillations. To ensure acceptable efficiency of the cascade process, a minimal ethanol concentration is defined and included as additional constraint in the controller design. The unmeasured state variables are estimated by using the asymptotic observer. It is shown that for smaller sampling times the predictive controllers are very effective, even in presence of parameter uncertainties. It is also observed that offset-free NMPC algorithm is more sensitive to measurement noise, but MS-NMPC and classical NMPC are more sensitive to estimation errors for longer sampling times.

Improvement of batch and continuous ethanol fermentations from sweet sorghum stem juice in a packed bed bioreactor by immobilized yeast cells under microaeration

Microaeration during ethanol fermentation from sweet sorghum stem juice (SSJ) by immobilized Saccharomyces cerevisiae NP01 was investigated in a tubular packed bed bioreactor to improve ethanol production. In batch fermentation from SSJ containing 230 g/L of total sugars, aeration time and its rate were optimized using a factorial design. The highest ethanol concentration (PE) and productivity (QP) was 106.9 g/L and 1.78 g/L·h, respectively, with sugar consumption (SC) of 89.9% under an aeration rate of 0.35 vvm for 12 h. In continuous ethanol fermentation under an aeration rate of 0.05 vvm, the initial sugar concentration and dilution rate were optimized for high values of SC, PE and QP using response surface methodology. The optimal conditions for continuous fermentation were an initial sugar concentration of 160 g/L and a dilution rate of 0.05 h−1, yielding satisfactory experimental values of SC, PE and QP values at 90.8%, 75.4 g/L and 3.72 g/L·h, respectively.

A robust flow cytometry-based biomass monitoring tool enables rapid at-line characterization of S. cerevisiae physiology during continuous bioprocessing of spent sulfite liquor

Assessment of viable biomass is challenging in bioprocesses involving complex media with distinct biomass and media particle populations. Biomass monitoring in these circumstances usually requires elaborate offline methods or sophisticated inline sensors. Reliable monitoring tools in an at-line capacity represent a promising alternative but are still scarce to date. In this study, a flow cytometry-based method for biomass monitoring in spent sulfite liquor medium as feedstock for second generation bioethanol production with yeast was developed. The method is capable of (i) yeast cell quantification against medium background, (ii) determination of yeast viability, and (iii) assessment of yeast physiology though morphological analysis of the budding division process. Thus, enhanced insight into physiology and morphology is provided which is not accessible through common online and offline biomass monitoring methods. To demonstrate the capabilities of this method, firstly, a continuous ethanol fermentation process of Saccharomyces cerevisiae with filtered and unfiltered spent sulfite liquor media was analyzed. Subsequently, at-line process monitoring of viability in a retentostat cultivation was conducted. The obtained information was used for a simple control based on addition of essential nutrients in relation to viability. Thereby, inter-dependencies between nutrient supply, physiology, and specific ethanol productivity that are essential for process design could be illuminated.Graphical abstract

FARKLI HİDROLİK ALIKONMA SÜRELERİNDE KEÇİBOYNUZU EKSTRAKTI BESİYERİNDE SÜREKLİ ETANOL FERMANTASYONU

Production of bioethanol is one of the important bioprocesses for the energy industry to provide inexpensive renewable resources all over the world. In this context, this research was organized for continuous ethanol fermentation from carob pod extract which is an inexpensive carbon source by free or immobilized S. cerevisiae cells. Continuous ethanol fermentations were performed with different HRT (from 4 to 20 h) and optimal HRT were 8 h for the free cell, and 6.67 h for immobilized cell, respectively. The highest volumetric ethanol productivities for free cell and immobilized cell fermentations were 3.12 g/L/h and 3.37 g/L/h at HRT of 5.71 h, respectively. All kinetic parameters clearly showed that both cell types can be used for ethanol fermentation, and immobilized S. cerevisiae ethanol fermentation can be operated at higher dilution rates independent of biomass than a free cell.

Genome Sequence of the Self-Flocculating Strain Saccharomyces cerevisiae SPSC01.

ABSTRACTThe self-flocculation of yeast cells presents advantages for continuous ethanol fermentation such as their self-immobilization within fermenters for high density to improve ethanol productivity and cost-effective biomass recovery by gravity sedimentation. We sequenced and analyzed the genome of the self-flocculating Saccharomyces cerevisiae SPSC01 for the industrial production of fuel ethanol.

Stability analysis of the continuous ethanol fermentation process with a delayed product inhibition

• A continuous ethanol fermentation system with a discrete delay is studied. • A delayed product inhibition is considered as a main reason for oscillatory behavior. • Effect of delay and product inhibition on the system behavior is discussed. In the paper, we propose and analyze a mathematical model of the continuous ethanol fermentation process to study the mechanisms of the self-sustained oscillations of ethanol concentration. The model is based on the assumption that microorganism cells response to the inhibitory effect of product (ethanol) concentration with a delay. From the local stability analysis of the system, we show that the delay time is one of the crucial factors for the occurrence of oscillations and for a critical delay time the fermentation process undergoes a Hopf bifurcation. Further analysis shows that the operating variables and kinetic parameters have also a significant effect on the dynamical behavior of the fermentation system. A proper manipulation of the operating variables allow us to eliminate the oscillatory behavior.

Improvement of a continuous ethanol fermentation from sweet sorghum stem juice using a cell recycling system

The process variables (aeration rate and recycle ratio) of a continuous ethanol fermentation with a cell recycling system (CRS) by Saccharomyces cerevisiae NP 01 from sweet sorghum stem juice were optimized using response surface methodology (RSM). The relationship between intracellular composition and fermentation efficiency was also investigated. RSM results revealed that the optimum aeration rate and recycle ratio were 0.25vvm and 0.625, respectively. The validation experiment under the optimum conditions indicated high precision and reliability of the experiment, achieving an actual ethanol concentration (PE) of 99.28g/l, which was very close to the predicted value (98.01g/l), and a very high ethanol productivity (QP) of 7.94g/lh. The intracellular composition of the yeast cells (i.e., unsaturated fatty acids (UFAs), total fatty acids (TFAs), ergosterol and trehalose) was positively related to the fermentation efficiency and yeast adaptive response under ethanol stress. A higher ratio of UFAs/TFAs and ergosterol strongly promoted yeast viability and ethanol fermentation. Additionally, high trehalose content was observed when the yeast was subjected to stress conditions.

Separation performance of novel vinyltriethoxysilane (VTES)-g-silicalite-1/PDMS/PAN thin-film composite membrane in the recovery of bioethanol from fermentation broths by pervaporation

Organophilic pervaporation (OPV) has been considered as one of the most promising separation processes for the recovery of biofuels from fermentation broths, however, in addition to preferred target product – liquid biofuels, the yeast cells and fermentation nutrients could affect the recovery efficiency of biofuels from broths by pervaporation. In this paper, the influence of the yeast cells and the fermentation nutrient components such as the sources of carbon, nitrogen and salts on the separation performance of the vinyltriethoxysilane (VTES)-grafted- (VTES-g-) silicalite-1/PDMS/PAN thin-film composite membrane was conducted systematically. The results revealed that glucose, xylose, protein, and salts cannot permeate through the membrane. Glucose concentration in the fermentation broth should be kept at a lower level (less than 20g/L) to eliminate its deleterious influence on ethanol flux and membrane selectivity. Xylose and corn steep liquor (CSL) have little effect on the pervaporation performance of the composite membrane. The addition of NaCl improved the membrane selectivity and ethanol flux but slightly lowered down total permeation flux. Adding dry yeast cells to the ethanol solution can enhance the turbulence in the feed mixtures, resulting an increase of the membrane flux and selectivity. The pervaporation performance of fermentation broths was also studied. The results showed that the nutrients and the deposition of yeast cells on the membrane surface didn’t deteriorate the pervaporation performance, indicating excellent fouling resistance of the novel VTES-g-silicalite-1/PDMS/PAN composite membrane in operation with fermentation broths. The continuous ethanol fermentation can be directly connected to the in-situ pervaporative recovery system without requiring prior removal of yeast cells.

Immobilization of Zymomonas mobilis with Fe2O3-modified polyvinyl alcohol for continuous ethanol fermentation

Zymomonas mobilis cells were immobilized with a novel Fe2O3-modified polyvinyl alcohol (PVA) matrix to perform continuous ethanol fermentation with very high efficiency. The key operating parameters, such as glucose feeding concentration, dilution rate, and cells loading were optimized to achieve high bioethanol production performance at a high dilution rate and high glucose utilization efficiency. The optimal conditions for ethanol fermentation with the modified PVA immobilized cells were determined as: cell loading, 40% (w/v); glucose feeding concentration, 125g/L; hydraulic retention time (HRT), 2h (or 0.5h⿿1 dilution rate). The bioethanol productivity was nearly doubled (31.09g/L/h) when the PVA-immobilized cells were modified with 1% (w/v) Fe2O3. The modified PVA-immobilized cells could be utilized for more than 20days without losing their activity.

Kinetic models for batch and continuous ethanol fermentation from sweet sorghum juice by yeast immobilized on sweet sorghum stalks

Kinetic models for batch and continuous ethanol fermentation from sweet sorghum juice by Saccharomyces cerevisiae NP 01 immobilized on unpeeled sweet sorghum stalk pieces were developed. The models accounted for substrate limitation, substrate inhibition, ethanol inhibition and cell death. Batch ethanol fermentations were done from juice containing various initial sugar concentrations (120–280g/L). The estimated values of the maximum specific growth rate (μmax) and Monod constant (Ks) were found to be 0.313h−1 and 47.51g/L, respectively, using a Lineweaver–Burk plot. These data were used to develop models for batch and continuous ethanol fermentation. For the batch fermentation, it was found that the models could be used to satisfactorily fit the experimental data for initial sugar concentrations ranging from 130 to 225g/L. However, for the continuous fermentation, only the data for substrate consumption and ethanol production were well fitted by the developed models.

Optimization of continuous ethanol fermentation from sweet sorghum juice by immobilized yeast cells under aerated culture

Optimization of continuous ethanol fermentation from sweet sorghum juice by immobilized yeast cells under aerated culture

Immobilized Kluyveromyces marxianus cells in carboxymethyl cellulose for production of ethanol from cheese whey: experimental and kinetic studies.

Cheese whey fermentation to ethanol using immobilized Kluyveromyces marxianus cells was investigated in batch and continuous operation. In batch fermentation, the yeast cells were immobilized in carboxymethyl cellulose (CMC) polymer and also synthesized graft copolymer of CMC with N-vinyl-2-pyrrolidone, denoted as CMC-g-PVP, and the efficiency of the two developed cell entrapped beads for lactose fermentation to ethanol was examined. The yeast cells immobilized in CMC-g-PVP performed slightly better than CMC with ethanol production yields of 0.52 and 0.49g ethanol/g lactose, respectively. The effect of supplementation of cheese whey with lactose (42, 70, 100 and 150g/l) on fermentative performance of K. marxianus immobilized in CMC beads was considered and the results were used for kinetic studies. The first order reaction model was suitable to describe the kinetics of substrate utilization and modified Gompertz model was quite successful to predict the ethanol production. For continuous ethanol fermentation, a packed-bed immobilized cell reactor (ICR) was operated at several hydraulic retention times; HRTs of 11, 15 and 30h. At the HRT of 30h, the ethanol production yield using CMC beads was 0.49g/g which implies that 91.07% of the theoretical yield was achieved.

Mathematical modeling of continuous ethanol fermentation in a membrane bioreactor by pervaporation compared to conventional system: Genetic algorithm

In this paper, genetic algorithm was used to investigate mathematical modeling of ethanol fermentation in a continuous conventional bioreactor (CCBR) and a continuous membrane bioreactor (CMBR) by ethanol permselective polydimethylsiloxane (PDMS) membrane. A lab scale CMBR with medium glucose concentration of 100gL−1 and Saccharomyces cerevisiae microorganism was designed and fabricated. At dilution rate of 0.14h−1, maximum specific cell growth rate and productivity of 0.27h−1 and 6.49gL−1h−1 were respectively found in CMBR. However, at very high dilution rate, the performance of CMBR was quite similar to conventional fermentation on account of insufficient incubation time. In both systems, genetic algorithm modeling of cell growth, ethanol production and glucose concentration were conducted based on Monod and Moser kinetic models during each retention time at unsteady condition. The results showed that Moser kinetic model was more satisfactory and desirable than Monod model.

Xylose fermentation efficiency and inhibitor tolerance of the recombinant industrial Saccharomyces cerevisiae strain NAPX37

Industrial yeast strains with good xylose fermentation ability and inhibitor tolerance are important for economical lignocellulosic bioethanol production. The flocculating industrial Saccharomyces cerevisiae strain NAPX37, harboring the xylose reductase-xylitol dehydrogenase (XR-XDH)-based xylose metabolic pathway, displayed efficient xylose fermentation during batch and continuous fermentation. During batch fermentation, the xylose consumption rates at the first 36h were similar (1.37g/L/h) when the initial xylose concentrations were 50 and 75g/L, indicating that xylose fermentation was not inhibited even when the xylose concentration was as high as 75g/L. The presence of glucose, at concentrations of up to 25g/L, did not affect xylose consumption rate at the first 36h. Strain NAPX37 showed stable xylose fermentation capacity during continuous ethanol fermentation using xylose as the sole sugar, for almost 1year. Fermentation remained stable at a dilution rate of 0.05/h, even though the xylose concentration in the feed was as high as 100g/L. Aeration rate, xylose concentration, and MgSO4 concentration were found to affect xylose consumption and ethanol yield. When the xylose concentration in the feed was 75g/L, a high xylose consumption rate of 6.62g/L/h and an ethanol yield of 0.394 were achieved under an aeration rate of 0.1 vvm, dilution rate of 0.1/h, and 5mM MgSO4. In addition, strain NAPX37 exhibited good tolerance to inhibitors such as weak acids, furans, and phenolics during xylose fermentation. These findings indicate that strain NAPX37 is a promising candidate for application in the industrial production of lignocellulosic bioethanol.

Ethanol fermentation integrated with PDMS composite membrane: An effective process

The polydimethylsiloxane (PDMS) membrane, prepared in water phase, was investigated in separation ethanol from model ethanol/water mixture and fermentation–pervaporation integrated process. Results showed that the PDMS membrane could effectively separate ethanol from model solution. When integrated with batch ethanol fermentation, the ethanol productivity was enhanced compared with conventional process. Fed-batch and continuous ethanol fermentation with pervaporation were also performed and studied. 396.2–663.7g/m2h and 332.4–548.1g/m2h of total flux with separation factor of 8.6–11.7 and 8–11.6, were generated in the fed-batch and continuous fermentation with pervaporation scenario, respectively. At the same time, high titre ethanol production of ∼417.2g/L and ∼446.3g/L were also achieved on the permeate side of membrane in the two scenarios, respectively. The integrated process was environmental friendly and energy saving, and has a promising perspective in long-terms operation.

Continuous ethanol fermentation in tower reactors with cell recycling using flocculent Saccharomyces cerevisiae

Alcoholic fermentation using yeast strains with flocculent characteristics results in a higher biomass concentration in the reactor than does the use of a culture without flocculation ability. In addition, this approach is economically competitive due to its simplicity and low cost, it requires no centrifugal separation for the soluble yeast cells and does not need support, as is the case with immobilized cells. This paper evaluates the behavior of a Saccharomyces cerevisiae strain with flocculent characteristics and the effect of altering the inlet sucrose concentration, flow cell recycle and residence time using a central composite design. A novel experimental process for ethanol fermentation was designed and evaluated by employing a cell-recycling two-tower-reactor system in which each tower was individually equipped with a settler for recycling flocculent yeast. The fermentation experiments were conducted in a system with two tower reactors, operated continuously in series. Fermentation yields of approximately 86% and productivity up to 18g/Lh were obtained in this process. The system was effective for continuous ethanol fermentation from sucrose, cane juice and molasses obtained from sugar manufacturing.

Production of ethanol from raw juice and thick juice of sugar beet by continuous ethanol fermentation with flocculating yeast strain KF-7

Sugar beet juice can serve as feedstock for ethanol product due to its high content of fermentable sugars and high energy output/input ratio. Batch ethanol fermentation of raw juice and thick juice proved that addition of mineral nutrients could not improve ethanol concentration, but could accelerate the fermentation rate. Fermentation of thick juice with an initial pH of 9.1 did not affect the fermentation process. The continuous ethanol fermentation of raw juice was performed at 35 °C with a dilution rate of 0.3 h−1, resulting in ethanol concentration, ethanol yield and productivity of 70.7 g L−1, 89.8% and 21.2 g L−1 h−1, respectively. A two-stage reactor was used in the continuous ethanol fermentation of thick juice by feeding fresh yeast cells into the second reactor. This process was stable at a total process dilution rate of 0.11 h−1 with an overall sugar concentration of 190 g L−1 in the influent. The ethanol concentration was kept at approximately 80 g L−1, corresponding to ethanol yield of 82.5% and productivity of 8.8 g L−1 h−1.

Ethanol Production from Cashew Apple Juice Using Immobilized Saccharomyces cerevisiae Cells on Silica Gel Matrix Synthesized from Sugarcane Leaf Ash

Ethanol is considered to be a promising alternative fuel to meet ever growing energy demands. In the present work, immobilized yeast cells by Saccharomyces cerevisiae were used for ethanol production from cashew apple juice as the substrate. The support, silica gel, was derived from a novel precursor sugarcane leaf ash. Sugarcane leaf is chosen due to its abundant availability, low cost, and also as a means to remove the agricultural residue. Substrate concentration, pH, and temperature have been optimized to achieve maximum production of ethanol. Maximum ethanol production was obtained at a substrate concentration of 70% (v/v), pH 6 and a temperature of 30°C. Maximum ethanol production was found to be 16,200 mg/L. Ethanol purity was determined and was found to be 97.79% pure (water free). Continuous ethanol fermentation was carried out in a packed bed reactor.