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A two-step pretreatment using sequential dilute acid/alkali was applied in this study to improve the hydrolysis of corncobs. 88.6% of the hemicellulose was selectively removed by dilute sulfuric acid hydrolysis (DA) in the first step, 88% of the lignin was effectively extracted by sodium hydroxide in the second step. Consequently, a high content of glucan (74.4%), corresponding to 94.6% recovery, remained in the pretreated biomass. The substrate enzymatic digestibilities (SED) of the two-step pretreated biomass were 64%, 80%, 91%, and 93% after 72 h hydrolysis with enzyme loadings of 5, 10, 15, and 20 FPU/g substrate, respectively, which were much higher than those of the DA-pretreated material. The ethanol concentration after the simultaneous saccharification and fermentation (SSF) process at 15% (w/w) solids loading reached 52 g/L, equivalent to 77.2% of the theoretical ethanol yield based on an untreated corncobs glucan content. The changes to the chemical and physical structures of the residues detected by SEM, FTIR, and the DPv test were correlated with the improved enzymatic digestibility. [ABSTRACT FROM AUTHOR]

In the present investigation, an collagen fibre (CF), abundant natural biomass, was successfully grafted by polyethyleneimine (PEI). The resultant PEI grafted collagen fibre (CF-PEI) was employed as biocompatible and high cell loading support matrix for the immobilization of Saccharomyces cerevisiae cells. The as-prepared CF-PEI immobilized cells (CF-PEI-cell) exhibited high activity and stability for both batch and continuous fermentation. In batch fermentation, CF-PEI-cells showed enhanced stability as compared with other matrices supported cells, and produced an average ethanol concentration of 45.04 g/L with ethanol yield (YP/S) of 0.46 g/g and glucose conversion efficiency (η) of 90.4%. Continuous fermentation was operated stably in a down-flow trickling bed reactor charged with CF-PEI-cell for a total of 2 months. When the dilution rate was 0.16 1/h, the average ethanol productivity reached 7.18 g/(L h) with η of 88.94%. Further scanning electron microscopy observations confirmed that yeast cells can proliferate on the surface of CF-PEI during ethanol fermentation, which demonstrates that CF-PEI is indeed an ideal matrix for the immobilization of yeast cells. [ABSTRACT FROM AUTHOR]

Since both ethanol and butanol fermentations are urgently developed processes with the biofuel-demand increasing, performance comparison of aerobic ethanol fermentation and anerobic butanol fermentation in a continuous and closed-circulating fermentation (CCCF) system was necessary to achieve their fermentation characteristics and further optimize the fermentation process. Fermentation and pervaporation parameters including the average cell concentration, glucose consumption rate, cumulated production concentration, product flux, and separation factor of ethanol fermentation were 11.45 g/L, 3.70 g/L/h, 655.83 g/L, 378.5 g/m2/h, and 4.83, respectively, the corresponding parameters of butanol fermentation were 2.19 g/L, 0.61 g/L/h, 28.03 g/L, 58.56 g/m2/h, and 10.62, respectively. Profiles of fermentation and pervaporation parameters indicated that the intensity and efficiency of ethanol fermentation was higher than butanol fermentation, but the stability of butanol fermentation was superior to ethanol fermentation. Although the two fermentation processes had different features, the performance indicated the application prospect of both ethanol and butanol production by the CCCF system. [ABSTRACT FROM PUBLISHER]

In this study, repeated-batch fermentations in a biofilm reactor were evaluated for ethanol production from non-sterile enriched (NSE) and non-sterile non-enriched (NSNE) carob extracts by usingSaccharomyces cerevisiae. For the NSE medium, the ethanol production (P) and yield (YP/S) were 18.46 g/L and 33.76%, respectively. However, for the NSNE medium,PandYP/Swere 19.57 g/L and 38.14%, respectively. Results indicated that cost-effective ethanol production from non-sterile carob extract (NSCE) can be successfully applied in a biofilm reactor regarding both energy cost and recovery time. [ABSTRACT FROM PUBLISHER]

The production of raw starch-degrading amylases by recombinant Saccharomyces cerevisiae provides opportunities for the direct hydrolysis and fermentation of raw starch to ethanol without cooking or exogenous enzyme addition. Such a consolidated bioprocess (CBP) for raw starch fermentation will substantially reduce costs associated with energy usage and commercial granular starch hydrolyzing (GSH) enzymes. The core purpose of this review is to provide comprehensive insight into the physiological impact of recombinant amylase production on the ethanol-producing yeast. Key production parameters, based on outcomes from modifications to the yeast genome and levels of amylase production, were compared to key benchmark data. In turn, these outcomes are of significance from a process point of view to highlight shortcomings in the current state of the art of raw starch fermentation yeast compared to a set of industrial standards. Therefore, this study provides an integrated critical assessment of physiology, genetics and process aspects of recombinant raw starch fermenting yeast in relation to presently used technology. Various approaches to strain development were compared on a common basis of quantitative performance measures, including the extent of hydrolysis, fermentation-hydrolysis yield and productivity. Key findings showed that levels of α-amylase required for raw starch hydrolysis far exceeded enzyme levels for soluble starch hydrolysis, pointing to a pre-requisite for excess α-amylase compared to glucoamylase for efficient raw starch hydrolysis. However, the physiological limitations of amylase production by yeast, requiring high biomass concentrations and long cultivation periods for sufficient enzyme accumulation under anaerobic conditions, remained a substantial challenge. Accordingly, the fermentation performance of the recombinant S. cerevisiae strains reviewed in this study could not match the performance of conventional starch fermentation processes, based either on starch cooking and/or exogenous amylase enzyme addition. As an alternative strategy, the addition of exogenous GSH enzymes during early stages of raw starch fermentation may prove to be a viable approach for industrial application of recombinant S. cerevisiae, with the process still benefitting from amylase production by CBP yeast during later stages of cultivation. [ABSTRACT FROM AUTHOR]

Ethanol fermentation from food waste could reduce the solid waste pollution and realize energy utilization. In order to decrease distillation waste, the recycle of such waste was adopted in ethanol fermentation. It demonstrated that such treatment could only last for four times due to the existence of side products. The distillation waste would gradually reduce ethanol concentration and sugar utilization ratio, lactic acid would be accumulated to 8 g/L, and salinity would be accumulated to 10 g/L, pH decreased to less than 3.5. Three-dimensional fluorescence analysis showed protein-type substances, microbial metabolism type substances, and humic substances were accumulated during the recycling. In order to resolve such problems, addition of protease was chosen in this research. The recycling time could enhance to seven times and the highest ethanol concentration was 35 g/L, the lowest ethanol concentration was 20 g/L. The recycling of distillation waste could save water resource, reduce wastewater discharges with high COD lees and reduce the cost. Which provided a new way for the clean production of bioethanol production from food waste. [ABSTRACT FROM PUBLISHER]

Effects of initial total soluble sugar concentrations on batch ethanol fermentation of sweet sorghum stalk juice bySaccharomyces cerevisiaestrain were investigated at initial total soluble sugar concentrations of 85–156 g/L. The result showed that cell growth and the ethanol yield were increased with the increase of initial total soluble sugar concentrations. The kinetic parameters at initial total soluble sugar concentrations of 85–156 g/L were obtained. With the increase of initial total soluble sugar concentration, an inhibition of initial total soluble sugar concentration on the maximum specific growth rate (μmax) was observed. However, the increase of initial total soluble sugar concentration favors in the increase of the maximum specific ethanol production rate (qmax). The models proposed by Hinshelwood were found to be appropriate for describing the batch growth and ethanol fermentation of sweet sorghum stalk juice by immobilizedSaccharomyces cerevisiaeat initial total soluble sugar concentrations of 85–156 g/L because the correlation coefficients for the cell growth kinetic model and the ethanol production kinetic model were greater than 0.99. [ABSTRACT FROM PUBLISHER]

The possibility of using whey permeate as a raw material for the production of ethanol by continuous fermentation by using Kluyveromyces marxianus was examined. The ethanol formation was investigated as a function of the hydraulic retention time in a UASB reactor. The initial lactose concentration in permeate was 50.0 g L-1. The hydraulic retention time supplied were 12, 24, 48 h and the daily ethanol formations were 4.46, 8.61, 7.73 g L-1, respectively. The yield coefficient of ethanol was 0.089 g ethanol g-1 lactose when the hydraulic retention time was 12 h and raised to 0.325 g g-1 when the hydraulic retention time was as long as 48 h. The results indicated that in ethanol fermentation the hydraulic retention time should be 24 h to obtain high rates of ethanol formation and to avoid product inhibition. [ABSTRACT FROM AUTHOR]

The technical feasibility of bioethanol production from reed, energy crop was evaluated by way of a simple acid treatment at a low temperature. The main goal of this study was to investigate the effect of various acid-to-biomass ratios, impregnation durations, and hydrolysis periods on conversion yield of reed to monomeric sugars and inhibitors production. As a result, the maximum glucan and xylan conversion yield, 90% and 95%, respectively, was obtained at 2:1 acid-to-biomass ratio, 5-h impregnation, and 2-h hydrolysis. The extreme acidity and increase in retention time under high temperature were the main factors to increase inhibitor concentration. Fermentation of reed-derived hydrolysate with Saccharomyces cerevisiae yielded 0.45 g-ethanol/g-glucose which is lower than that of the reference fermentation (0.49 g/g) due to inhibitors; HMF, furfural, acetic acid, and formic acid. [ABSTRACT FROM AUTHOR]

The main factors, including temperature, agitation rate, pH, and particles stuffing rate, were chosen in ethanol fermentation from stalk juice of sweet sorghum using immobilized S. cerevisiae in shaking flasks in order to determine suitable conditions. The results showed that a temperature of 34°C, agitation rate of 150-200 r · min-1, pH of 4.5, and particles stuffing rate of 25% should be selected as the suitable condition. The results of verification experiments at the selected condition demonstrated that the ethanol yield, the CO2 weight loss rate, and fermentation time were 95.15%, 0.508 g · h-1, and 6 h in the shaking flasks, respectively. Meanwhile, the ethanol yield and the fermentation time were 96.72% and 10 h in the 5 L bioreactor. As a result, it could be concluded that the determined condition was suitable and reasonable for ethanol fermentation from by immobilized S. cerevisiae. [ABSTRACT FROM AUTHOR]