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Very high gravity (VHG) ethanol fermentation at low temperatures can be a way to obtain wines with high ethanol content (> 15 °GL). The production of vinasse is lower, compared to typical industrial conditions, which reduces the costs of storage and transport. However, there is greater heat generation during cell growth, resulting in an increased requirement for cooling water. One promising way to cool the vat is to use CO2 stripping, which removes heat by vaporization of the ethanol and water in the broth. Therefore, the aim of the present study was to find suitable operating conditions, considering the gas flow rate ( F CO 2 ) and the stripping start ( t start ) and stop ( t stop ) times, that could reduce the volume of water required for temperature control. Simulations of extractive fermentations at 28 and 34 °C, with must substrate concentration ( C SM ) of 300 g/L, were performed to obtain F CO 2 , t start , and t stop . Experimental validations showed water volume reductions of 66.4% (28 °C) and 67.0% (34 °C), compared to the corresponding conventional ethanol fermentations. An extractive VHG fermentation at 28 °C, with C SM =372 g/L, was carried out under the conditions obtained in the simulations. The results showed a 61.9% reduction in water volume and a total ethanol content of 15 °GL. The gas stripping technique applied to VHG fermentation at low temperature was proved to be environmentally friendly, since it reduced the volume of vinasse generated and saved water, which could reduce the number of heat exchangers and the costs associated with their maintenance. [ABSTRACT FROM AUTHOR]

Cassava (Manihot esculenta Crantz) leaves contain high protein content (ca 20%). This study aimed to evaluate application of the leaves as a nitrogen source for Saccharomyces cerevisiae in ethanol fermentation by comparing it with general nitrogen sources in yeast malt (YM) media. Mild pretreatments: liquid hot water, alkaline, and dilute acid, were conducted to extract amino nitrogen from the leaves while minimizing degradation. The liquid fraction from the liquid hot water pretreatment (CLWP) showed the highest amino nitrogen content of 271 ± 25 mg of N/L. Most free amino acids in CLWP were glutamic acid (22 g/kg leaves) and aspartic acid (20 g/kg leaves). After 24 h of fermentation, the equal glucose and nitrogen concentration media with CLWP gave 5 times higher ethanol content (10% v/v) than the absence of CLWP conditions (2% v/v). Free amino acids in the leaves provided a greater benefit to yeasts in ethanol production than other traditional chemical sources. Cassava leaves had high potential to be used as a nitrogen source for ethanol fermentation. [ABSTRACT FROM AUTHOR]

The consolidation of cellulosic ethanol on the market is fundamental to mitigate the consumption of fuels from fossil sources and to reduce the impact caused by the large generation of agro-industrial waste. In order to achieve this objective, some challenges of cellulosic ethanol technology must be overcome, including the improvement of the cellulosic ethanol production steps. Several studies propose the use of poly(ethylene glycol) (PEG) and non-ionic surfactants (such as Tween 80, Tween 20, and Triton X-100) as a way to increase cellulosic ethanol titers. The benefits attributed to the PEG and non-ionic surfactants go beyond the increase of the concentration of free cellulases during enzymatic hydrolysis. Successful cases of pretreatments of lignocellulosic biomasses assisted by PEG and surfactants and the detoxification of inhibitor-rich hydrolysates with PEG reveal the existence of a plethora of positive mechanisms. Therefore, the present review article is focused on the benefits and mechanisms involved in the addition of PEG and non-ionic surfactants in the pretreatment, enzymatic hydrolysis, and ethanol fermentation steps. Interactions between additives and lignin as well as schemes based on high PEG concentrations were also discussed in detail. [ABSTRACT FROM AUTHOR]

Toxin-tolerant yeast strains that produce high ethanol yield are inevitably requited for cost-effective ethanol production from undetoxified steam-exploded corn stover. To verify the ethanol-producing capability of the strain Saccharomyces cerevisiae Y5 developed in our laboratory, simultaneous saccharification and fermentation of undetoxified steam-exploded corn stover with solids loading of 30 % ( w/ v) was carried out in different-sized flasks and an automatic fermenter. After 96 h, the ethanol concentrations had reached 50, 47.8, and 47.5 g/L in the 100-mL flask, 3,000-mL flask, and 5-L automatic fermenter, respectively. The experiment demonstrates that ethanol production from undetoxified steam-exploded corn stover using S. cerevisiae Y5 simplifies the production process, reduces equipment investment and water consumption, and generates highly concentrated ethanol. S. cerevisiae Y5 is a promising strain that could reduce the cost of producing ethanol from steam-exploded corn stover. [ABSTRACT FROM AUTHOR]

The thermotolerant strain Saccharomyces cerevisiae DQ1 was applied to the simultaneous saccharification and fermentation (SSF) at high temperature and high solids loading of the dilute acid-pretreated corn stover in the present study. The SSF using S. cerevisiae DQ1 was operated at 30 % solids loading of the pretreated corn stover with three-step SSF mode and achieved up to ethanol titer of 48 g/L and yield of 65.6 %. S. cerevisiae DQ1 showed strong thermotolerance in both the regular one-step SSF and the three-step SSF with changing temperature in each step. The three-step SSF at 40°C using S. cerevisiae DQ1 tolerated the greater cellulase dosage and solids loading of the pretreated corn stover and resulted in increased ethanol production. The present study provided a practical potential for the future SSF of lignocellulose feedstock at high temperature to reach high ethanol titer. [ABSTRACT FROM AUTHOR]

Integration of first- and second-generation ethanol production is a strategy to strengthen the economic viability of individual processes and the overall viability of biorefineries. The sharing of storage, fermentation, distillation, and energy infrastructure is an important advantage of process integration. Furthermore, integration contributes to the utilization and valorization of all products and by-products, which is key to the success of a biorefinery. Selenium-enriched yeasts have aroused great interest as mineral sources for their high bioavailability and low toxicity. This study aimed to evaluate the effect of selenium on yeast cell growth and production of ethanol and xylitol from hydrolyzed hemicellulosic biomass and sugarcane molasses. For this, cultures were enriched with sodium selenite at concentrations ranging from 1 to 20 mg/L. A miniaturization protocol was used to simulate biorefinery production of first-generation ethanol. The yeasts Spathaspora passalidarum and Kluyveromyces marxianus were able to grow under all tested conditions. The maximum specific growth rate, lag time, and biomass production were influenced by selenium concentration. S. passalidarum provided the best fermentation results, with 77.9% ethanol fermentation efficiency, 24.7% xylitol fermentation efficiency, 0.25 g/g glycerol yield, and 3.3 g cell biomass production. K. marxianus accumulated 122.92 mg selenium/kg biomass, whereas S. passalidarum had a maximum accumulation of 37.40 mg selenium/kg biomass. Yeasts also accumulated other minerals. Therefore, S. passalidarum has great potential as a biological platform and the results of this work could be useful for supporting the development of integrated processes to produce ethanol-, xylitol-, glycerol-, and selenium-enriched yeast products. [ABSTRACT FROM AUTHOR]

The sustainability of bioethanol production depends on substrate selection. Since direct fermentation allows the interaction between antinutrients and microbes, antinutrient content becomes a crucial factor for substrate selection as these components possess growth inhibitory effects on sensitive microbes. This study demonstrated that the growth of Klebsiella sp. SWET4 had been significantly affected by antinutrients like phytate (3.09% reduction per µg‧mL−1), phenolic acid (0.222% reduction per µg‧mL−1), cyanide (0.376% reduction per µg‧mL−1), and tannin (0.038% reduction per µg‧mL−1). The correlation study of the effect of antinutrients on bacterial growth was further analyzed by principal component analysis (PCA) confirming the least growth inhibitory effect exhibited by banana peel as compared to other selected substrates. Based on the literature survey, genes or gene products that could be affected by selected antinutrient were successfully localized in the genome of SWET4, confirming the severe effect of these antinutrients on bacterial growth. The kinetic study of SWET4 also revealed the fact that ethanol production was growth-associated as derived from the Luedeking-Piret model, both in glucose supplemented and banana peel supplemented culture broths. This also implied that ethanol production was proportional to bacterial growth which can also be maximized in substrates containing the least antinutrients. Hence, for the selection of the best suitable substrates for bioethanol production by direct fermentation technique, the growth inhibitory components should be one of the principal criteria. [ABSTRACT FROM AUTHOR]

Effective pretreatment is essential for successfully utilizing renewable resources such as lignocellulosic biomass in the production of bioethanol. In this study, ternary deep eutectic solvents (DESs), namely choline chloride/lactic acid/glycerol (ChCl/LA/Gly), choline chloride/oxalic acid/glycerol (ChCl/OA/Gly), choline chloride/lactic acid/ethylene glycol (ChCl/LA/EG), and choline chloride/oxalic acid/ethylene glycol (ChCl/OA/EG) were prepared and employed for the pretreatment of cellulose-rich Napier grass (NG). Post treatment, the NG hydrolysate was subjected to enzymatic saccharification followed by ethanol fermentation. The results showed effective delignification of NG after treatment with the prepared ternary DESs, with ChCl/LA/EG removing a maximum of 92.89% lignin. The efficiency of the prepared DESs is attributed to their low densities, pH, and viscosity. Enzymatic saccharification of ChCl/LA/EG-treated NG resulted in a 1.68 fold increase in reducing sugar yield compared to that of untreated NG. All pretreated NG produced more bioethanol via a separate hydrolysis and fermentation (SHF) process than untreated NG after Saccharomyces cerevisiae fermentation. A maximum of 0.37 g bioethanol/g of biomass was obtained from the one-pot process using ChCl/LA/Gly pretreatment. FTIR and XRD analyses of untreated and pretreated NG corroborated the efficacy of the ternary DESs on cellulose recovery and delignification. Also, enzymatic and microbial inhibition studies on the prepared DESs show their potential to be employed in a one-pot process for biorefinery. The results of the present investigation show the potential of utilizing eco-friendly DESs and renewable resources for the production of bioethanol, a viable option to fossil fuels. [ABSTRACT FROM AUTHOR]

Spathaspora passalidarum is a naturally pentose-fermenting yeast with the potential to be applied for biotransformation of sugars from lignocellulosic biomasses. Despite being mostly investigated for ethanol production from sugarcane bagasse sugars (mainly xylose and glucose), this microorganism is also capable of producing high xylitol concentrations as a by-product of the ethanol fermentation. The integration of ethanol and xylitol production can improve the economic viability of the process due to the lower sale price of ethanol and the higher added-value of xylitol, a sucrose-substitute sugar with healthier properties. Considering the metabolic pathways interaction from glucose and xylose, it is essential to understand the effect of different glucose and xylose concentrations in the production of ethanol and xylitol by S. passalidarum. In this way, a simultaneous production of both products for the development of an integrated platform for food and chemical and biofuel industries can be accessed. Yeast biomass can also be recovered and applied as a protein source. Therefore, in this study, the fermentative performance of S. passalidarum was investigated in batch fermentations with different xylose and glucose concentrations, using synthetic substrate. The ATP levels and the enzymatic activities of xylose reductase (XR), xylitol dehydrogenase (XDH), and alcohol dehydrogenase (ADH) were also determined for each condition. The results indicated that low amounts of glucose (35%) were necessary to promote a higher xylitol production (10.58 ± 0.29 g/L) without losses on ethanol yield (78.99 ± 4.41%), being the most interesting condition for simultaneous formation of both products. [ABSTRACT FROM AUTHOR]

Marine algae are promising third-generation feedstocks for bioethanol production as they are fast growing, require minimal inputs, and do not compete for land. However, marine algae have complex cell walls which necessitate pretreatment prior to fermentation, and this represents a major component of the cost of bioethanol production. Standard pretreatment processes using acids are costly and generate hazardous waste streams. This study aims to develop an economic and environmentally friendly pretreatment process using ozonolysis for the marine algae Kappaphycus alvarezii and Gelidium amansii. Acid and ozone pretreatments were compared across the pretreatment, enzyme hydrolysis, and fermentation stages of bioethanol production. Acid pretreatment outperformed ozonolysis over the pretreatment and enzyme hydrolysis stages. However, it also generated as by-products the compounds 5-hydroxymethyl furfural (5-HMF) and levulinic acid (LA), which inhibited ethanol fermentation and reduced the efficiency of the process overall. Ozone pretreatment did not produce these inhibitory compounds, and as such outperformed acid pretreatment across the process as a whole. These results indicate the potential of ozonolysis as an economic and environmentally friendly pretreatment for the production of bioethanol from marine algae. [ABSTRACT FROM AUTHOR]

Cassava (Manihot esculenta) is a woody bush extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates. The main residue from its cultivation is the cassava stalk, which is normally used as soil fertilizer or in culture propagation. The main goal of this paper is to evaluate two routes (biochemical and thermochemical) for bioenergy production (ethanol and synthesis gas—electricity) using cassava stalk as raw material. A detailed techno-economic and energy assessment is carried out based on the simulation approach of both conversion routes to determine the production costs of main products and the overall energy efficiency of the processes. The electricity production costs vary from 0.008 to 0.037 USD/MJ, whereas the ethanol production costs range from 1.11 to 2.02 USD/L (including subsidies). The change in the production costs was observed due to the assumptions of the model, e.g., cassava stalk, transportation, and enzyme costs. The overall energy efficiency of the gasification and ethanol fermentation was 68.7 and 25.1%, respectively. [ABSTRACT FROM AUTHOR]

This study reports on the evaluation of a two-stage pretreatment process for preparing cotton gin trash (CGT) for conversation to ethanol. During the first stage, CGT was mixed with acid at 12% H2SO4 on solids and heated to 180 °C for 15 min in a pressurised stirred reactor. Pressed first-stage pretreated fibres were heated to 200 °C for 5 min during the second stage. The two-stage process facilitated excellent sugar recovery from both cellulose (84%) and hemicellulose (78%) fractions of CGT. Recombinant yeast GSF335 propagated on first-stage liquors yielded 41.8 g kg−1 of dry CGT and was compared with the commercial yeast during separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentations (SSF). SHF of pretreated CGT fibre yielded the equivalent of 66.2 and 64.0 kg ethanol per tonne of unprocessed CGT with GSF335 and the commercial yeast, respectively. SSF ethanol yields for the commercial yeast were significantly lower (50.3 kg) while GSF335 correspondingly produced 63.8 kg ethanol per tonne of raw CGT. [ABSTRACT FROM AUTHOR]

Reducing the cost of cellulosic ethanol production, especially the use of expensive exogenous cellulose hydrolytic enzymes such as cellulase and β-glucosidase, is a critical challenge and vital for a sustainable advanced biofuel industry. Here, we report a novel ethanologenic yeast strain Clavispora NRRL Y-50464 that produces sufficient innate β-glucosidase enzyme activity for cellulosic ethanol production by simultaneous saccharification and fermentation (SSF). In a bottled SSF, strain Y-50464 produced 40.44 g/L ethanol from pure cellulose within 72 h at a conversion rate of 0.04 g/L/h, applying conventional cellulase without supplementary β-glucosidase. Ethanol conversion from delignified corn stover by Y-50464 showed significantly higher titers and rates at various solids loading levels than that from conventional pretreated corn stover with over 40 to 60 % improved efficiency in a bottled SSF. However, the bottled SSF was inefficient for mixing higher levels of cellulose feedstock and should be replaced by a more suitable experimental apparatus. In a 2-L bioreactor SSF using conventional dilute acid pretreated corn stover, strain Y-50464 produced 32 g/L ethanol from 20 % solids loading at 48 h applying cellulase alone without addition of β-glucosidase. This represented a conversion rate of 0.088 g/L/h, the highest rate so far for cellulosic ethanol production from lignocellulosic materials. Elimination of β-glucosidase in cellulose-to-ethanol fermentation would be expected to reduce cost of cellulose conversion. The robustness, fast growth rate, and the capability of producing both ethanol and β-glucosidase illustrated the potential of strain Y-50464 as a potential candidate biocatalyst for advanced biofuel production from lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

Methods to increase the energy density of biofuel feedstock for shipment are important towards improving supply chain efficiency in upstream processes. Towards this end, densified pretreated lignocellulosic biomass was produced using hot-pressing. The effects of fiber hornification induced by hot-pressing on enzymatic digestibilities of lodgepole pine and poplar NE222 wood chips pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) were examined. Pretreated wood chips were pressed at 25, 70, 90, 110, and 177 °C. The cellulose accessibilities of the pressed and unpressed substrates were evaluated using water retention value and direct cellulase adsorption measurements. Hot-pressing below 110 °C produced a degree of hornification (DH) below 0.26 and had limited effect on cellulose accessibility and enzymatic digestibility. Hot-pressing at 177 °C produced a DH of 0.86 that substantially hornified the fibers and resulted near zero saccharification. The saccharification results were consistent with cellulose accessibility data. Ethanol fermentation studies at 18 % solids suggest that a pressing below 110 °C is preferred to reduce its effect on biofuel yield. [ABSTRACT FROM AUTHOR]

A coproduct of dry-grind ethanol fermentation, corn distillers' dried grains with solubles (DDGS) represents a low-cost feedstock with potential to integrate production of biodiesel and ethanol. Oil extracted from DDGS was converted into distillers' grains methyl (DGME) and ethyl (DGEE) esters. Pretreatment using sulfuric acid was effective at lowering the acid value of the crude oil from 27.15 to less than 0.30 mg KOH g, thus rendering it amenable to homogenous, base-catalyzed transesterification. Measurement of fuel properties and comparison to refined corn oil methyl (RCME) and ethyl (RCEE) esters revealed that the cold flow properties and oxidative stability of DGME and DGEE were deficient relative to RCME and RCEE. In the absence of antioxidants, DGME and DGEE did not meet the oxidative stability specifications of ASTM D6751 and EN 14214. The cetane number of DGEE was below the minimum limit specified in EN 14214. DGEE exhibited more favorable cold flow properties, iodine value, and energy content than DGME. Evaluation of blends (B5 and B20) in petroleum diesel fuel revealed that antioxidants and cetane enhancers would be required to meet the specifications of the US and European diesel fuel standards. Other fuel properties of the petrodiesel blends were largely neutral with respect to alkyl ester type and conformed to the limits specified in the respective standards. [ABSTRACT FROM AUTHOR]