Fuel Ethanol Production Research Articles

Enhanced fuel ethanol production from rice straw hydrolysate by an inhibitor-tolerant mutant strain of Scheffersomyces stipitis

A novel process for bioethanol production from lignocellulosic biomass using an inhibitor-tolerant mutant strain of Scheffersomyces stipitis and cell-recycling continuous fermentation.

Coutilization of D-Glucose, D-Xylose, and L-Arabinose in Saccharomyces cerevisiae by Coexpressing the Metabolic Pathways and Evolutionary Engineering

Efficient and cost-effective fuel ethanol production from lignocellulosic materials requires simultaneous cofermentation of all hydrolyzed sugars, mainly including D-glucose, D-xylose, and L-arabinose. Saccharomyces cerevisiae is a traditional D-glucose fermenting strain and could utilize D-xylose and L-arabinose after introducing the initial metabolic pathways. The efficiency and simultaneous coutilization of the two pentoses and D-glucose for ethanol production in S. cerevisiae still need to be optimized. Previously, we constructed an L-arabinose-utilizing S. cerevisiae BSW3AP. In this study, we further introduced the XI and XR-XDH metabolic pathways of D-xylose into BSW3AP to obtain D-glucose, D-xylose, and L-arabinose cofermenting strain. Benefits of evolutionary engineering: the resulting strain BSW4XA3 displayed a simultaneous coutilization of D-xylose and L-arabinose with similar consumption rates, and the D-glucose metabolic capacity was not decreased. After 120 h of fermentation on mixed D-glucose, D-xylose, and L-arabinose, BSW4XA3 consumed 24% more amounts of pentoses and the ethanol yield of mixed sugars was increased by 30% than that of BSW3AP. The resulting strain BSW4XA3 was a useful chassis for further enhancing the coutilization efficiency of mixed sugars for bioethanol production.

Production of Ethanol From Newly Developed and Improved Winter Barley Cultivars.

Winter barley has attracted strong interest as a potential feedstock for fuel ethanol production in regions with mild winter climate such as the mid-Atlantic and northeastern USA. Ten recently developed and improved winter barley cultivars and breeding lines including five hulled and five hull-less lines were experimentally evaluated for potential ethanol production. The five hulled barley lines included three released cultivars (Thoroughbred, Atlantic, and Secretariat) and two breeding lines (VA09B-34 and VA11B-4). The five hull-less lines also included three released cultivars (Eve, Dan, and Amaze 10) and two breeding lines (VA08H-65 and VA13H-34). On the average, the hull-less barley cultivars produced more ethanol per unit mass because of their higher starch and β-glucan contents. However, since the hulled barley cultivars had higher agronomic yield, the potential ethanol production per acre of land for the two types were approximately equal. Among the ten cultivars tested, the hull-less cultivar Amaze 10 was the best one for ethanol production. The ethanol yield values obtained for this cultivar were 2.61gal per bushel and 292gal per acre.

Anhydrous fuel ethanol production by a combined hydrophobic–hydrophilic pervaporation system

ABSTRACTIn this study, a hybrid bioethanol production and purification system was designed and operated at different operation conditions. In the first stage, dilute ethanol (3 wt%) was produced by fermentation and concentrated to 80 wt% ethanol–water mixture by means of poly(dimethylsiloxane) membrane. In the second stage, residual water was purified to approximately 99% water content by using carboxymethyl cellulose membrane. The first stage is a fermentor, so the temperature was kept stable at 25°C. Effects of the operation variables such as temperature and concentration of the mixture on membrane separation performance were evaluated.

Evaluation of fuel ethanol production from aqueous ammonia-treated rice straw via simultaneous saccharification and fermentation

Rice straw (RS) has been considered a promising feedstock for ethanol production in Asia. However, the recalcitrance of biomass, particularly the presence of lignin, hinders the enzymatic saccharification of polysaccharides in RS and consequently decreases the ethanol yield. Here, we used aqueous ammonia pretreatment to remove lignin from RS (aRS). The reaction conditions were a solid:liquid ratio of 1:12, an ammonia concentration of 27% (w w−1), room temperature, and a 2-week incubation. We evaluated enzymatic digestibility and the ethanol production yield. A 42% reduction in lignin content increased the glucan conversion of aRS to glucose from 20 to 71% using a combination of Cellic Ctec2 cellulases and Cellic Htec2 xylanases at enzyme loads of 15 FPU +100 XU g−1 solid. Scanning electron microscopy highlighted the extensive removal of external fibres and increased porosity of aRS, which aided the accessibility of cellulose for enzymes. Using the same enzyme dosage and a solid load of 100 g L−1, simultaneous saccharification and fermentation using a monoculture of Saccharomyces cerevisiae and co-culture with Candida tropicalis yielded ethanol concentrations of 22 and 25 g L−1, corresponding to fermentation efficiencies of 96 and 86% fermentation, respectively. The volumetric ethanol productivities for these systems were 0.45 and 0.52 g L−1 h−1. However, the ethanol yield based on the theoretical glucose and xylose concentrations was lower for the co-culture (0.44 g g−1) than the monoculture (0.49 g g−1) due to the low xylose consumption. Further research should optimise fermentation variables or select/improve microbial strains capable of fermenting xylose to increase the overall ethanol production yield.

Fate of virginiamycin through the fuel ethanol production process.

Antibiotics are frequently used to prevent and treat bacterial contamination of commercial fuel ethanol fermentations, but there is concern that antibiotic residues may persist in the distillers grains coproducts. A study to evaluate the fate of virginiamycin during the ethanol production process was conducted in the pilot plant facilities at the National Corn to Ethanol Research Center, Edwardsville, IL. Three 15,000-liter fermentor runs were performed: one with no antibiotic (F1), one dosed with 2 parts per million (ppm) of a commercial virginiamycin product (F2), and one dosed at 20 ppm of virginiamycin product (F3). Fermentor samples, distillers dried grains with solubles (DDGS), and process intermediates (whole stillage, thin stillage, syrup, and wet cake) were collected from each run and analyzed for virginiamycin M and virginiamycin S using a liquid chromatography-mass spectrometry method. Virginiamycin M was detected in all process intermediates of the F3 run. On a dry-weight basis, virginiamycin M concentrations decreased approximately 97 %, from 41 μg/g in the fermentor to 1.4 μg/g in the DDGS. Using a disc plate bioassay, antibiotic activity was detected in DDGS from both the F2 and F3 runs, with values of 0.69 μg virginiamycin equivalent/g sample and 8.9 μg/g, respectively. No antibiotic activity (<0.6 μg/g) was detected in any of the F1 samples or in the fermentor and process intermediate samples from the F2 run. These results demonstrate that low concentrations of biologically active antibiotic may persist in distillers grains coproducts produced from fermentations treated with virginiamycin.

De novo analysis of transcriptome reveals genes associated with leaf abscission in sugarcane (Saccharum officinarum L.).

BackgroundSugarcane (Saccharum officinarum L.) is an important sugar crop which belongs to the grass family and can be used for fuel ethanol production. The growing demands for sugar and biofuel is asking for breeding a sugarcane variety that can shed their leaves during the maturity time due to the increasing cost on sugarcane harvest.ResultsTo determine leaf abscission related genes in sugarcane, we generated 524,328,950 paired reads with RNA-Seq and profiled the transcriptome of new born leaves of leaf abscission sugarcane varieties (Q1 and T) and leaf packaging sugarcane varieties (Q2 and B). Initially, 275,018 transcripts were assembled with N50 of 1,177 bp. Next, the transcriptome was annotated by mapping them to NR, UniProtKB/Swiss-Prot, Gene Ontology and KEGG pathway databases. Further, we used TransDecoder and Trinotate to obtain the likely proteins and annotate them in terms of known proteins, protein domains, signal peptides, transmembrane regions and rRNA transcripts. Different expression analysis showed 1,202 transcripts were up regulated in leaf abscission sugarcane varieties, relatively to the leaf packaging sugarcane varieties. Functional analysis told us 62, 38 and 10 upregulated transcripts were involved in plant-pathogen interaction, response to stress and abscisic acid associated pathways, respectively. The upregulation of transcripts encoding 4 disease resistance proteins (RPM1, RPP13, RGA2, and RGA4), 6 ABC transporter G family members and 16 transcription factors including WRK33 and heat stress transcription factors indicate they may be used as candidate genes for sugarcane breeding. The expression levels of transcripts were validated by qRT-PCR. In addition, we characterized 3,722 SNPs between leaf abscission and leaf packaging sugarcane plants.ConclusionOur results showed leaf abscission associated genes in sugarcane during the maturity period. The output of this study provides a valuable resource for future genetic and genomic studies in sugarcane.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2552-2) contains supplementary material, which is available to authorized users.

Fuel ethanol production from commercial grain sorghum cultivars with different tannin content

The two-step enzymatic starch hydrolysis of three commercial sorghum grain cultivars (Flash 10 Plus, 8419 and Flash 1) containing different tannin content (<0.2%, 1.1% and 2.0% respectively) was evaluated, in order to determine the most promising process for the production of ethanol. High viscosities were obtained for suspensions of the three cultivars (6440–8071 cP). The hydrolysis efficiency values were two and three times greater in the cultivars with higher tannin content (8419 and Flash 1, respectively) when a gelatinization step previous to starch hydrolysis was performed, reaching similar values for the three cultivars (87%–88%); for the low-tannins cultivar a lower improvement was observed. The addition of a protease, pepsin, which could disrupt the interaction between the protein and starch, did not improve the starch hydrolysis efficiency. Simultaneous saccharification and ethanol fermentation (SSF) assays were carried out. The removal of tannins improved the performance of the SSF, suggesting that this treatment may have eliminated inhibitors and also contributed to a partial depolymerization or loss of crystallinity of starch. For a 1:3 solid–liquid ratio, an ethanol concentration of 107 g/L at 68 h, a fermentation efficiency of 100% and an industrial yield of 390 L/t of sorghum (dry basis) were obtained.

Production of bioethanol as useful biofuel through the bioconversion of water hyacinth (Eichhornia crassipes).

Water hyacinth (Eichhornia crassipes) represents a promising candidate for fuel ethanol production in tropical countries because of their high availability and high biomass yield. Bioconversion of such biomass to bioethanol could be wisely managed through proper technological approach. In this work, pretreatment of water hyacinth (10 %, w/v) with dilute sulfuric acid (2 %, v/v) at high temperature and pressure was integrated in the simulation and economic assessment of the process for further enzymatic saccharification was studied. The maximum sugar yield (425.6 mg/g) through enzymatic saccharification was greatly influenced by the solid content (5 %), cellulase load (30 FPU), incubation time (24 h), temperature (50 °C), and pH (5.5) of the saccharifying medium. Central composite design optimized an ethanol production of 13.6 mg/ml though a mixed fermentation by Saccharomyces cerevisiae (MTCC 173) and Zymomonas mobilis (MTCC 2428). Thus the experiment imparts an economic value to water hyacinths that are cleared from choking waterways.

New methods for positive selection of yeast ethanol overproducing mutants

AbstractFuel ethanol is an environmentally friendly alternative liquid fuel to the widely used petroleum derived transportation liquid fuels. Since 2007, worldwide fuel ethanol production has increased. Currently ethanol is primarily produced from carbohydrates such as sucrose and starch by fermentation using the yeast Saccharomyces cerevisiae. In this work, new approaches for the selection of S. cerevisiae strains with increased ethanol production from hydrolyzed corn meal are described. An industrial production strain of Saccharomyces cerevisiae AS400 was subjected to positive selection of mutants resistant to toxic concentrations of oxythiamine, trehalose, 3-bromopyruvate, glyoxylic acid, and glucosamine. The selected mutants are characterized by 5-8% increase in ethanol yield (g g-1 of consumed glucose) as compared to the parental industrial ethanol-producing strain. A three-step selection approach that consisted of the use of glyoxylic acid, glucosamine and bromopyruvate resulted in a 12% increase in ethanol yield during fermentation on industrial media. These results indicate that the selected strains are promising candidates for industrial ethanol production.

Energy and GHG balances of ethanol production from cane molasses in Indonesia

This study analyses the sustainability of fuel ethanol production from cane molasses in Indonesia. Life cycle assessment (LCA) is performed to evaluate the net emissions (climate change impact) and energy inputs (resource consumption) in the production chain. The lifecycle greenhouse gas (GHG) emissions in the production and use of ethanol are estimated at 29gCO2eq per MJ of ethanol produced which is a 67% reduction in comparison to gasoline emissions. Net Energy Value (NEV) and Net Renewable Energy Value (NREV) are −7MJ/l and 17.7MJ/l, while the energy yield ratio (ER) is 6.1. Economic allocation is chosen for dividing environmental burdens and resource consumption between sugar (i.e. main product) and molasses (i.e. co-product used for fuel production). Sensitivity analysis of various parameters is performed. The emissions and energy values are highly sensitive to sugarcane yield, ethanol yield, and the price of molasses. The use of sugarcane biomass residues (bagasse/trash) for efficient cogeneration, and different waste management options for the treatment of spent wash (effluent of distilleries) are also explored. Surplus bioelectricity generation in the efficient cogeneration plant, biogas recovery from wastewater treatment plant, and their use for fossil fuel substitution can help improve energy and environmental gains. The study also compares important results with other relevant international studies and discusses issues related to land use change (LUC) impact.

New approaches for improving the production of the 1st and 2nd generation ethanol by yeast.

Increase in the production of 1st generation ethanol from glucose is possible by the reduction in the production of ethanol co-products, especially biomass. We have developed a method to reduce biomass accumulation of Saccharomyces cerevisiae by the manipulation of the intracellular ATP level due to overexpression of genes of alkaline phosphatase, apyrase or enzymes involved in futile cycles. The strains constructed accumulated up to 10% more ethanol on a cornmeal hydrolysate medium. Similar increase in ethanol accumulation was observed in the mutants resistant to the toxic inhibitors of glycolysis like 3-bromopyruvate and others. Substantial increase in fuel ethanol production will be obtained by the development of new strains of yeasts that ferment sugars of the abundant lignocellulosic feedstocks, especially xylose, a pentose sugar. We have found that xylose can be fermented under elevated temperatures by the thermotolerant yeast, Hansenula polymorpha. We combined protein engineering of the gene coding for xylose reductase (XYL1) along with overexpression of the other two genes responsible for xylose metabolism in yeast (XYL2, XYL3) and the deletion of the global transcriptional activator CAT8, with the selection of mutants defective in utilizing ethanol as a carbon source using the anticancer drug, 3-bromopyruvate. Resulted strains accumulated 20-25 times more ethanol from xylose at the elevated temperature of 45°C with up to 12.5 g L(-1) produced. Increase in ethanol yield and productivity from xylose was also achieved by overexpression of genes coding for the peroxisomal enzymes: transketolase (DAS1) and transaldolase (TAL2), and deletion of the ATG13 gene.

Cost evaluation of cellulase enzyme for industrial-scale cellulosic ethanol production based on rigorous Aspen Plus modeling.

Cost reduction on cellulase enzyme usage has been the central effort in the commercialization of fuel ethanol production from lignocellulose biomass. Therefore, establishing an accurate evaluation method on cellulase enzyme cost is crucially important to support the health development of the future biorefinery industry. Currently, the cellulase cost evaluation methods were complicated and various controversial or even conflict results were presented. To give a reliable evaluation on this important topic, a rigorous analysis based on the Aspen Plus flowsheet simulation in the commercial scale ethanol plant was proposed in this study. The minimum ethanol selling price (MESP) was used as the indicator to show the impacts of varying enzyme supply modes, enzyme prices, process parameters, as well as enzyme loading on the enzyme cost. The results reveal that the enzyme cost drives the cellulosic ethanol price below the minimum profit point when the enzyme is purchased from the current industrial enzyme market. An innovative production of cellulase enzyme such as on-site enzyme production should be explored and tested in the industrial scale to yield an economically sound enzyme supply for the future cellulosic ethanol production.

Implementation of an Indirect Control Structure for Composition in a Hybrid Distillation Column

In this paper a PID controller is proposed to ensure the fuel ethanol composition at desired value, above 92.5°INPM, at the same time as saving energy through the minimal use of reboiler power. Due to the fact that composition analyzers are expensive and have a high response time, an inference model was developed in which the product composition is inferred from the product temperature and thermodynamics equations, enabling the monitoring and the indirect control a posteriori of this variable. In addition, the inference of composition allows defining the reference value of the product temperature, which ensures the fuel ethanol production at the desired composition.

Cassava stem wastes as potential feedstock for fuel ethanol production: A basic parameter study

The cassava stem is found to be one of few crop residues containing starch (up to 42% of dry mass) that may be converted to fuel ethanol. The current study was to evaluate the influence of parameters genotype, growth location and harvest time on cassava stem starch contents and yields as well as consequences in ethanol production (non-cellulosic process), based on 180 samples from a full factorial design experiment (3 varieties × 3 locations × 5 harvest times) in Guangxi, China. The potential utilization of stem starch and soluble sugar that varied 14–42% and 3–12.1% of dry mass, respectively, can correspond to an increase of 26% in ethanol production compared to that produced by roots only. The cassava stem starch content was significantly affected by all three studied parameters and location had the largest effect followed by variety and harvest time, while the stem starch yield was significantly affected by location only. The starch and soluble sugar content were significantly correlated with soil properties, e.g., soil pH and organic carbon, S and P contents. A general and positive correlation was also found between the stem and root starch, suggesting a promising potential of using stem starch without reducing root starch production.

Evaluating the bioenergy potential of cassava on marginal land using a biogeochemical process model in GuangXi, China

Bioenergy is expected to play an important role in future energy systems. Cassava is believed to be one of the most promising energy plants for fuel ethanol production in the tropics and subtropics. In China, plant-based bioenergy has to be developed on marginal land to avoid impacting food security. Cassava yield varies dramatically under different environmental conditions. Therefore, an efficient approach is needed to estimate cassava yield on marginal land. This paper presents a method for assessing the energy potential of cassava using a biogeochemical process model. First, the spatial distribution of marginal land was identified. A geographic information system-based biogeochemical process model, the GIS-based environmental policy integrated climate model, was used to simulate the spatial and temporal dynamics of the major processes of the soil-cassava-atmosphere management system. The model was calibrated and successfully applied to data from GuangXi province, Southwest China. The results indicated that the potential bioenergy of cassava on marginal land under rain-fed conditions in GuangXi province is 1,909,593.96 million MJ, which is equivalent to the energy of 17.0844 million tons of standard coal; the potential energy of irrigated cassava is 2,054,017.73 million MJ, which is equivalent to the energy of 18.3765 million tons of standard coal.

Airborne measurements of the atmospheric emissions from a fuel ethanol refinery

AbstractEthanol made from corn now constitutes approximately 10% of the fuel used in gasoline vehicles in the U.S. The ethanol is produced in over 200 fuel ethanol refineries across the nation. We report airborne measurements downwind from Decatur, Illinois, where the third largest fuel ethanol refinery in the U.S. is located. Estimated emissions are compared with the total point source emissions in Decatur according to the 2011 National Emissions Inventory (NEI‐2011), in which the fuel ethanol refinery represents 68.0% of sulfur dioxide (SO2), 50.5% of nitrogen oxides (NOx = NO + NO2), 67.2% of volatile organic compounds (VOCs), and 95.9% of ethanol emissions. Emissions of SO2 and NOx from Decatur agreed with NEI‐2011, but emissions of several VOCs were underestimated by factors of 5 (total VOCs) to 30 (ethanol). By combining the NEI‐2011 with fuel ethanol production numbers from the Renewable Fuels Association, we calculate emission intensities, defined as the emissions per ethanol mass produced. Emission intensities of SO2 and NOx are higher for plants that use coal as an energy source, including the refinery in Decatur. By comparing with fuel‐based emission factors, we find that fuel ethanol refineries have lower NOx, similar VOC, and higher SO2 emissions than from the use of this fuel in vehicles. The VOC emissions from refining could be higher than from vehicles, if the underestimated emissions in NEI‐2011 downwind from Decatur extend to other fuel ethanol refineries. Finally, chemical transformations of the emissions from Decatur were observed, including formation of new particles, nitric acid, peroxyacyl nitrates, aldehydes, ozone, and sulfate aerosol.

A preliminary study of sugaring-out extraction coupled with ethanol fermentation for separating ethanol from fermentation broth

In order to solve the high energy consumption of fuel ethanol production and wastewater treatment, a new technology of sugaring-out ethanol extraction from broth coupled with ethanol fermentation using raffinate phase was presented. Ethanol recovery reached 70% in both simulated ethanol fermentation broth and actual broth using one time sugaring-out extraction, while the initial concentrations of glucose, butanol and ammonium sulfate were 10%, 30%, and 2%, respectively. The influence of raffinate phase on ethanol fermentation was also investigated, and its showed that after butanol concentration decreased to 6.5 g/L by CO2 stripping of raffinate phase, the raffinate phase could be recycled as backset. Along with the increase of raffinated phase cycle numbers, ethanol fermentation time, ethanol concentration and yield were prolonged and decreased, which indicated that sugaring-out ethanol extraction from broth coupled with ethanol fermentation need to be further improved.

Efficient enzymatic hydrolysis and simultaneous saccharification and fermentation of sugarcane bagasse pulp for ethanol production by cellulase from Penicillium oxalicum EU2106 and thermotolerant Saccharomyces cerevisiae ZM1-5

Sugarcane bagasse (SB) is a promising alternative feedstock for second-generation fuel ethanol production. Chemical SB pulp has high cellulose content (73.89%) and low lignin content (0.49%). SB pulp and pretreated SB were subjected to digestion by cellulase produced by Penicillium oxalicum EU2106. The results showed that SB pulp released the highest amount of reducing sugars, when compared with other pretreated SB. The glucan conversion reached 93.36% after 96 h hydrolysis of SB pulp at an enzyme loading of 20 FPU/g solid and a solid loading of 60 g/L. Thermotolerant Saccharomyces cerevisiae ZM1-5 was employed in simultaneous saccharification and fermentation of SB pulp to ethanol, which was performed in multiple parallel fermentation tanks (500 mL working volume). A considerable amount of ethanol (18.79 g/L at 0.42 g ethanol/g cellulose) was produced when the solid loading was 60 g/L. All data indicated that SB pulp could be employed as an alternative material for bioethanol production.

Simplified process for preparation of schizophyllan solutions for biomaterial applications

ABSTRACTSchizophyllan is a biopolymer commercially produced for pharmaceutical and cosmetics uses. However, schizophyllan also has potential biomaterial applications. Schizophyllan is conventionally produced from glucose and recovered by diafiltration and ultrafiltration to produce a highly purified product. Here we demonstrate a simplified process for preparation of schizophyllan solutions for biomaterial applications. Schizophyllan was produced in 1.5-L bioreactors from distiller’s dried grains with solubles (DDGS), an abundant coproduct of dry grind fuel ethanol production. Downstream processing eliminated filtration and concentration steps, providing solutions containing 4.2 ± 0.3 g schizophyllan/L. Solutions contained high-molecular-weight schizophyllan and exhibited viscosity properties similar to those of commercial schizophyllan. Schizophyllan solutions showed promise as a component of biolubricants in friction and wear tests and by dynamic surface and interfacial tension measurements.