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Increasing ethanol demand and public concerns about environmental protection promote the production of lignocellulosic bioethanol. Compared to that of starch- and sugar-based bioethanol production, the production of lignocellulosic bioethanol is water-intensive. A large amount of water is consumed during pretreatment, detoxification, saccharification, and fermentation. Water is a limited resource, and very high water consumption limits the industrial production of lignocellulosic bioethanol and decreases its environmental feasibility. In this review, we focused on the potential for reducing water consumption during the production of lignocellulosic bioethanol by performing pretreatment and fermentation at high solid loading, omitting water washing after pretreatment, and recycling wastewater by integrating bioethanol production and anaerobic digestion. In addition, the feasibility of these approaches and their research progress were discussed. This comprehensive review is expected to draw attention to water competition between bioethanol production and human use.

The use of fruit residues from domestic consumption for energy purposes is a perspective of innovation in the search for a more sustainable fuel, due to the low cost of this biomass, combined with its large amounts of generation, which has sugars readily available in its composition and does not require process pretreatment hydrolysis complexes of the material. This work evaluated residues of melon, pineapple, banana, apple, and mango, to compose a mixture of fruit waste (MFW), simulating a household waste for bioethanol production by a non-conventional yeast Wickerhamomyces sp. UFFS-CE-3.1.2. Sugar extraction was optimized by experimental design (MFW: 12% g dry mass v−1; 25 °C; 5 min) and resulted in the liberation of 36.32 ± 0.72 g L−1 fermentable sugar. MFW was used for alcoholic fermentation with and without nitrogen supplementation (urea and yeast extract). The results demonstrated that it is not necessary for the supplementation, making the process more economically viable. The maximum ethanol productivity (2.50±0.06 g L−1 h−1) was achieved in 9 h of the operation. The MFW extracted is an alternative for the bioethanol process as low cost and straightforward, adapted for different fruit residues, and used as a unique or diluent medium in the biorefinery context. Moreover, non-conventional yeast demonstrated the more new one in this study that explores the potential of yeast recently isolated.

The use of lignocellulosic biomass as feedstock in the production of second generation of bioethanol has gained significant attention due to environmental sustainability concern and the rising issue of global waste. The biomass is typically hydrolysed to release the fermentable sugars that will further utilized in ethanol fermentation. However, bioethanol production from lignocellulosic biomass still struggling with the separation and purification of the biomass hydrolysates. The main obstacle is to deal with the inhibitory compounds that generated along with sugar molecules during hydrolysis process. Inhibitors such as acetic acid, formic acid, furfural and HMF are toxic for the downstream process of bioethanol production and must be removed prior to the fermentation step. Recently, nanofiltration membrane shows a great potential in biorefineries of small molecules like sugars. The optimum efficiency of this membrane technology is influenced by many factors such as transport mechanism, membrane materials, and the operating conditions such as temperature, pH, pressure, feed concentration. Thus, this paper will comprehensively review the effect of these parameters on the nanofiltration performance that mainly reflected by permeate flux and solute rejection. The present paper also outlines the challenges and outlook of membrane technology on saccharide recovery for improvement of the membrane productivity.

Banana (M. acuminata x balbisiana) is an abundant lignocellulosic waste material in large plantations all over the Philippines, especially in Mindanao, which can be utilized as substrate in producing high-value products like ethanol. To compensate for the low yield based on total weight of substrate due to the high moisture content of banana pseudostem, there is the primary challenge to make the conversion of this lignocellulosic biomass into monomeric sugar and then into ethanol more efficiently in order to achieve yields that would make it cost-competitive. Hence, this study evaluated the effects of solid loading, incubation time and amount of enzyme on yield of reducing sugars in the enzymatic hydrolysis process and attempted to optimize the significant factors by Response Surface Methodology (RSM), specifically using Box-Behnken design. There was significant improvement on the reducing sugar yield of the pretreated banana pseudostem at 20 h incubation time, 15 g solid loading and 0.55 % enzyme concentration. Ethanol production was observed to be higher in the detoxified substrate although biomass was higher for the non-detoxified substrate. As to our knowledge, the present study is the first attempt to produce second generation ethanol using banana pseudostem waste as feedstock in the Philippines.

In this study, various mathematical functions were utilized to fit the observed values and the kinetic parameters of fermentation in immobilized-cell stirred tank reactor (ICSTR) with carob extract medium (CEM). The best model was selected based on the residual sum of squares (RSS), root-mean-square-error (RMSE), mean-absolute-error (MAE), determination coefficient (R2), slope (m), bias factor (BF), accuracy factor (AF), the objective function (Φ-factor), and f-testing. Therefore, the Stannard (ST) model was good agreement with the actual biomass production (X), ethanol production (P), and sugar consumption (S) data (RSS = 0.22, 6.23, and 45.70 g/L; RMSE = 0.17, 0.88, and 2.39 g/L; MAE = 0.14, 0.64, and 1.72 g/L; R2 = 0.9948, 0.9977, and 0.9972; m = 1.03, 1.02, and 1.02; BF = 1.35, 1.08, and 0.97; AF = 1.41, 1.14, and 1.04; and Φ-factor = 0.008, 0.004, and 0.005 (∑Φ-factor = 0.017) for X, P, and S, respectively). In the prediction of kinetic parameters belonging to the experimental fermentation, the ST model also gave better, satisfactory, and well-directed results than the other mathematical models. Besides, the ST model was also accomplishedly validated using two independent sets of the experimental data yielded from the different carbon sources in various concentrations. Consequently, the models proposed for X, P, and S can serve as universal functions to predict the real values and the kinetic parameters of the ethanol fermentation. Besides, these models can be applied to improve the ethanol fermentation in the ICSTR with CEM.

Cactus pear biomass has the potential for bioethanol production in dry regions. However, its low solids concentration and pH variations may hinder the process of alcoholic fermentation. The objectives of this study were as follows: (1) to evaluate the effects of harvest time and season on biomass pH and dry matter concentration of cladodes of two cactus pear species commonly used as forage (Nopalea cochenillifera and Opuntia stricta); (2) to compare the hydrolysis of fresh and dried biomass (10% w v−1 solids); (3) to compare increasing periods of two temperatures (65 °C or 105 °C) to concentrate the biomass to 10% and 30% solids; and (4) to perform enzymatic hydrolysis and fermentation of biomass dried to 30% solids. Biomass pH ranged from 3.0 to 5.6, from early morning to late afternoon, with higher diurnal variation during the dry season, when their solids concentrations were higher than in the rainy season (12–16% × 7–10%). Hydrolyzed fresh and dried biomass had similar glucose, xylose, and galacturonic acid concentrations. Drying at 105 °C for 12 h was the best temperature and period to reach 30% of solids. The enzymatic hydrolysis of the biomass dried to 30% solids yielded 65.3 and 80.0 g of glucose L−1. After fermentations (33 °C; 8 h; Saccharomyces cerevisiae), ethanol was produced to 29.4 and 37.5 g L-1 from N. cochenillifera and O. stricta biomasses, respectively. Therefore, early morning during the dry season is the best moment to harvest the cladodes, whose biomass can be partially dried at 105 °C for 12 h to 30% solids load before being hydrolyzed and fermented for bioethanol production. This procedure reduces the time, energy, and inputs needed in the process.

Solid-state fermentation, featured by water-saving, eco-friendly and high concentration product, is a promising technology in lignocellulosic ethanol industry. However, in solid-state fermentation system, large gas content inside the substrate directly leads to high oxygen partial pressure and inhibits ethanol fermentation. Z. mobilis can produce ethanol from glucose near the theoretical maximum value, but this ethanol yield would be greatly decreased by high oxygen partial pressure during solid-state fermentation. In this study, we applied N2 periodic pulsation process intensification (NPPPI) to ethanol solid-state fermentation, which displaced air with N2 and provided a proper anaerobic environment for Z. mobilis. Based on the water state distribution, the promotion effects of NPPPI on low solid loading and solid-state fermentation were analyzed to confirm the different degrees of oxygen inhibition in ethanol solid-state fermentation. During the simultaneous saccharification solid-state fermentation, the NPPPI group achieved 45.29% ethanol yield improvement and 30.38% concentration improvement compared with the control group. NPPPI also effectively decreased 58.47% of glycerol and 84.24% of acetic acid production and increased the biomass of Z. mobilis. By coupling the peristaltic enzymatic hydrolysis and fed-batch culture, NPPPI made the ethanol yield and concentration reach 80.11% and 55.06 g/L, respectively, in solid-state fermentation.

Dilute acid pretreatment produced a considerable amount of carbonyl compounds in the biomass prehydrolysates, which significantly inhibited the sequential microbial fermentation. To reduce the rele...

Weak acids are known to have a negative impact on yeast performance, restraining production efficiency during the production of bioethanol and other fermentative yeast-derived products. These acids, which might be hydrophilic or lipophilic exert negative effects on yeasts when they diffuse into the cell in their unionized state as a result of their pH being lower than the pka of yeast growth medium. Consequently, the unionized acids dissociate into their respective cations and anions, as intracellular pH is typically neutral. Further, proton accumulation tends to reduce intracellular pH. As a result, the anions destabilize the internal cell machinery, thus affecting cellular metabolism on various levels. Overcoming this acid-mediated stress in budding yeast would in part, harness the potential of using lignocellulosic biomass hydrolysate – which is typically acetic acid-rich – as a cheaper feedstock for large-scale bioethanol production. Since organic acids are key intermediates in ethanol fermentation, this review focuses on the prospects of bioethanol production from lignocellulosic biomass using weak acid-tolerant strains of yeasts derived by metabolic engineering.

New substrates and fermentation conditions have been drawing researchers’ attention to increase the bioethanol productivity. The aim of this study was to evaluate the acid hydrolysis of Spirulina biomass and its use in association with molasses in ethanol production with and without magnetic field (MF) application. Hydrothermal hydrolysis of Spirulina biomass hydrolysis was evaluated. The highest reducing sugar concentration (79% w w−1) was obtained with sulfuric acid 5% (v v−1), 121 °C, 30 min, and 500 g L−1 of biomass. This hydrolyzed biomass and molasses were used as substrates in the alcoholic fermentation with Saccharomyces cerevisiae by varying the biomass/molasses (B/M) ratio: 25, 50, and 75% (v v−1). The medium 25% B/M had higher ethanol yield at 78.9% and productivity of 0.72 g L−1 h−1. MF application did not increase the cell growth and ethanol production. This is the first study that integrates molasses and microalgal biomass substrates for ethanol production and presents some new information about magnetic fields application that is still little explored in the literature.

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.

Ethanol is one of the most important platform chemicals that can be produced in a continuous biofilm reactor. The continuous system can be easily adapted to a biofilm reactor, which is a useful tool for ethanol production by microorganisms. In this study, two different media (the first medium: acid-pretreated/detoxified and glucose-enriched rice husk hydrolysate; the second medium: acid-pretreated/detoxified and xylose-enriched rice husk hydrolysate) were used for ethanol production in a continuous biofilm reactor. Both medium (1.5 L) were supplemented with 1% (w/v) yeast extract and 2% (w/v) peptone. The dilution rate for the first medium was between 0.02 and 0.12 h−1, while for the second medium, it was between 0.01 and 0.05 h−1. When the first medium was used for ethanol fermentation in a continuous system, maximum ethanol productivity of 0.418 g/L/h and maximum biomass productivity of 0.196 g/L/h were yielded at dilution rates of 0.08 and 0.10 h−1, respectively. As for the second medium for ethanol fermentation in a continuous system, their values were 0.083 and 0.079 g/L/h at dilution rates of 0.03 and 0.04 h−1, respectively. Additionally, the yield factors for biomass and ethanol (Y0X/S and Y0P/S) were also found to be 0.642 g X/g S and 0.49 g P/g S for the first medium and 0.254 g X/g S and 0.27 g P/g S for the second medium, respectively. In addition, although cost-effective ethanol production regarding energy cost and recovery time is desired, the use of the non-enriched sterile and enriched non-sterile media in a repeated-batch biofilm reactor caused low fermentation kinetics. Consequently, ethanol production was successfully performed by using Scheffersomyces stipitis in a continuous PCS-biofilm reactor including acid-pretreated/detoxified and glucose- or xylose-enriched rice husk hydrolysate, which gave higher ethanol concentration compared with subsequent ethanol fermentation in a repeated-batch biofilm reactor.

Background The growth of the cellulosic ethanol industry is currently impeded by high production costs. One possible solution is to improve the performance of fermentation itself, which has great potential to improve the economics of the entire production process. Here, we demonstrated significantly improved productivity through application of an advanced fermentation approach, named self-cycling fermentation (SCF), for cellulosic ethanol production. Results The flow rate of outlet gas from the fermenter was used as a real-time monitoring parameter to drive the cycling of the ethanol fermentation process. Then, long-term operation of SCF under anaerobic conditions was improved by the addition of ergosterol and fatty acids, which stabilized operation and reduced fermentation time. Finally, an automated SCF system was successfully operated for 21 cycles, with robust behavior and stable ethanol production. SCF maintained similar ethanol titers to batch operation while significantly reducing fermentation and down times. This led to significant improvements in ethanol volumetric productivity (the amount of ethanol produced by a cycle per working volume per cycle time)—ranging from 37.5 to 75.3%, depending on the cycle number, and in annual ethanol productivity (the amount of ethanol that can be produced each year at large scale)—reaching 75.8 ± 2.9%. Improved flocculation, with potential advantages for biomass removal and reduction in downstream costs, was also observed. Conclusion Our successful demonstration of SCF could help reduce production costs for the cellulosic ethanol industry through improved productivity and automated operation.

Thiswork aimed to describe fermentation characteristics of ethanol productivity by the hybrids of baker's yeast. In this study five parental isolates and 15 genotypic hybrids of Saccharomyces cerevisiae derived from three crosses were used for estimating fermentation characteristics during bioethanol production. At 0.02 concentration of sugarcane sub- products the hybrids of P1 x P4 increased turbidity and pH value above the mid–parent. In contrast, biomass formation showed decline production. However, at 0.04 and 0.06 sugarcane sub- products some of the hybrids increased significantly pH value above the mid–parent indicating that fermentation profile differs from one concentration of dissolved solids to another. However, ethanol productivity was affected mainly by low pH, high acidity, high alcohol content, high temperature and osmotic pressure. The low pH was the main stress factor on yeast during fermentation. Though, the hybrids derived from the cross between P2 x P5 significantly increased pH value above the mid – parent at 0.02 and 0.04 concentration of sugarcane sub–products. The yeast hybrids showed better turbidity and biomass formation at 0.02 concentration if compared with the mid–parents and the higher concentrations of sugarcane sub–products. Most hybrids derived from the cross between P3 x P5 showed significant pH values above the mid – parents at all concentrations of sugarcane sub- products. In addition, most hybrids showed significant turbidity above the mid – parents at 0.02 sub–products. However, insignificant differences were shown between yeast genotypes for turbidity and biomass formation at 0.04 and 0.06 concentration of dissolved solids.

Construction of acid-tolerant strains of Saccharomyces cerevisiae is required for various bioproduction processes. We previously isolated the gene IoGAS1 from multiple stress-tolerant Issatchenkia orientalis as a gene conferring sulfuric acid resistance in S. cerevisiae, but its acid tolerance was only investigated using sulfuric acid. Here, we evaluated the growth and ethanol fermentation ability of the IoGAS1-expressing S. cerevisiae strain, B4-IoGAS1, by using various acidic reagents. B4-IoGAS1 exhibited faster growth than the control strain, B4-CON, when cultured aerobically with sulfuric, hydrochloric, formic, acetic, and lactic acids at pH below 2.4. However, the growth of B4-IoGAS1 was suppressed at pH above 2.48, irrespective of the type of acid reagents. Furthermore, B4-IoGAS1 exhibited higher performance of ethanol fermentation than B4-CON under 250 mM lactic acid condition at pH 2.37. These results demonstrate that IoGAS1 could facilitate the aerobic growth and anaerobic ethanol production under different acidic stressed conditions.

The integrated production of bioethanol and biogas makes it possible to optimise the production of carriers from renewable raw materials. The installation analysed in this experimental paper was a hybrid system, in which waste from the production of bioethanol was used in a biogas plant with a capacity of 1 MWe. The main objective of this study was to determine the energy potential of biomass used for the production of bioethanol and biogas. Based on the results obtained, the conversion rate of the biomass—maize, in this case—into bioethanol was determined as the efficiency of the process of bioethanol production. A biomass conversion study was conducted for 12 months, during which both maize grains and stillage were sampled once per quarter (QU-I, QU-II, QU-III, QU-IV; QU—quarter) for testing. Between 342 L (QU-II) and 370 L (QU-I) of ethanol was obtained from the organic matter subjected to alcoholic fermentation. The mass that did not undergo conversion to bioethanol ranged from 269.04 kg to 309.50 kg, which represented 32.07% to 36.95% of the organic matter that was subjected to the process of bioethanol production. On that basis, it was concluded that only two-thirds of the organic matter was converted into bioethanol. The remaining part—post-production waste in the form of stillage—became a valuable raw material for the production of biogas, containing one-third of the biodegradable fraction. Under laboratory conditions, between 30.5 m3 (QU-I) and 35.6 m3 (QU-II) of biogas per 1 Mg of FM (FM—fresh matter) was obtained, while under operating conditions, between 29.2 m3 (QU-I) and 33.2 m3 (QU-II) of biogas was acquired from 1 Mg of FM. The Biochemical Methane Potential Correction Coefficient (BMPCC), which was calculated based on the authors’ formula, ranged from 3.2% to 7.4% in the analysed biogas installation.

Optimization of the continuous fermentation process is important for increasing efficiency and decreasing cost, especially for complicated biochemical processes described by substrate and product inhibition. The optimum design (minimum volume) of CSTRs in series assuming substrate and product inhibition was determined in this study. The effect of operating parameters on the optimum design was investigated. The optimum substrate concentration in the feed to the first reactor was determined for N reactors in series. The nonlinear, constrained optimization problem was solved using the MATLAB function “fmincon”. It was found that the optimum design is more beneficial at high substrate conversion and at a medium level of feed substrate concentration. The best number of reactors is two to three for optimum arrangements and two for equal-size arrangements. The presence of biomass in the feed to the first reactor reduces the reactor volume, while the presence of product in the feed slightly increases the required total volume. The percentage reduction in the total volume using the optimum design compared to equal-volume design (R%) was determined as a function of substrate conversion and substrate concentration in the feed to the first reactor. The obtained R% values agree with experimental data available in the literature for ethanol fermentation.

In this paper, the effect of a variable temperature fermentation model was studied. We identified a model which considers substrate, product, and biomass inhibition, as well as an active and inactive cell phase of the yeast Saccharomyces cerevisiae. The model was evaluated using MATLAB at five different temperatures (28, 31, 34, 37, and 40°C). In the proposed model, we optimized the results through parameter fitting and compared it to the initial model which failed to simulate cell death. Through this work, we were able to improve the fit of the model considerably by 33% decrease, in the residual standard deviation. We also found that a smaller range of temperature performs better by maintaining the ethanol concentration and decreasing the temperature through the fermentation. Our model can show fermentation over a change in temperature over time and can show how fermentations will perform with temperature change.

In this study, introduction of a viable cell sensor and electronic nose into ethanol fermentation was investigated, which could be used in real-time and on-line monitoring of the amount of living cells and product content, respectively. Compared to the conventional off-line biomass determination, the capacitance value exhibited a completely consistent trend with colony forming units, indicating that the capacitance value could reflect the living cells in the fermentation broth. On the other hand, in comparison to the results of off-line determination by high-performance liquid chromatography, the ethanol concentration measured by electronic nose presented an excellent consistency, so as to realize the on-line monitoring during the whole process. On this basis, a dynamic feeding strategy of glucose guided by the changes of living cells and ethanol content was developed. And consequently, the ethanol concentration, productivity and yield were enhanced by 15.4%, 15.9% and 9.0%, respectively. The advanced sensors adopted herein to monitor the key parameters of ethanol fermentation process could be readily extended to an industrial scale and other similar fermentation processes.

Background: The bioethanol produced from biomass is a promising alternative fuel. The lignocellulose from marginal areas or wasteland could be a promising raw material for bioethanol production because it is present in large quantities, is cheap, renewable and has favorable environmental properties. Despite these advantages, lignocellulosic biomass is much more difficult to process than cereal grains, due to the need for intensive pretreatment and relatively large amounts of cellulases for efficient hydrolysis. Therefore, there is a need to develop an efficient and cost-effective method for the degradation and fermentation of lignocellulosic biomass to ethanol. Results: The usefulness of lignocellulosic biomass from wasteland for the production of bioethanol using pretreatment with the aid of ionic liquids of 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride was evaluated in this study. The pretreatment process, enzymatic hydrolysis and alcoholic fermentation lasted a total of 10 d. The largest amounts of bioethanol were obtained from biomass originating from agricultural wasteland, in which the dominant plant was fireweed (Chamaenerion angustifolium) and from the field where the common broom (Cytisus scoparius) was the dominant. Conclusions: The plants such as fireweed, common broom, hay and goldenrod may be useful for the production of liquid biofuels and it would be necessary in the further stage of research to establish and optimize the conditions for the technology of ethyl alcohol producing from these plant species. Enzymatic hydrolysis of biomass from agricultural wastelands results in a large increase in fermentable sugars, comparable to the enzymatic hydrolysis of rye, wheat, rice or maize straw.How to cite: Smuga-Kogut M, Piskier T, Walendzik B, et al. Assessment of wasteland derived biomass for bioethanol production. Electron J Biotechnol 2019;41. https://doi.org/10.1016/j.ejbt.2019.05.001. Keywords: Bioethanol, Biofuels, Biomass, Biorefineries, Cellulases, Fuels, Hemicellulose, Hydrolysis, Ionic liquid, Lignin, Lignocellulose, Wasteland

Este trabajo tiene como objetivo principal obtener etanol mediante fermentación alcohólica aplicando procesos biotecnológicos; debido a su alto contenido en azucares se emplea el mosto de uva como sustrato y la levadura Saccharomyces cerevisiae como agente biológico para completar la fermentación, debido a que, este microorganismo ha sido probado en investigaciones anteriores mostrando una elevada tolerancia al etanol. Se tuvo en cuenta variables como el pH, tiempo de fermentación, los grados Brix, formación de biomasa, entre otros. Los rendimientos de etanol y biomasa fueron de 0,483 gg-1 y 0,069 gg-1, respectivamente, además se establecieron las dimensiones del reactor en la escala industrial asumiendo una producción de 30L de etanol. Palabras clave: etanol, fermentación, mosto de uva.

KOH (1%) and glycerol (20–40%) pretreatment of bamboo, rubber, elephant grass and nSiam weed were investigated with respect to biomass composition, enzymatic hydrolysis and ethanol fermentation. Delignification was higher under alkaline environment and increased considerably with temperature (25-121 °C). Lignin removal had a positive effect on biomass digestibility, sugars production and ethanol yield. The highest sugar and ethanol yields were observed for KOH pretreatment (121 °C, 1 h) on elephant grass which also recorded the highest delignification (67.5%) and consequently the lowest solids recovery (59.5%). The grass gave the highest yield on glucose (19 g/100 g raw material), xylose (8.2 g/100 g raw material) and ethanol (9.8 g/100 g raw material) under KOH pretreatment (121 °C, 1 h). The elephant grass has great potential to be used as a major energy crop in Africa in a biorefinery where production of sugars, ethanol and other valuable biochemicals are optimised.

The search for a balance between the energy-related challenges of the future and providing nutritional security has resulted in the development of a market for biofuels of successive generations. The larger their portion in biofuel production, the less the prices of agricultural products will increase. The use of algae, cyanobacteria and aquatic plants in the production of liquid fuels is an alternative. The aim of this study was to determine the effect of thermal hydrolysis on degradation of polysaccharides contained in biomass of cyanobacteria Arthrospira platensis and to assess the effectiveness of ethanol production from preconditioned biomass. The study is aimed at the selection of the most advantageous parameters of thermochemical hydrolysis to reach the experiment variant with the best effects, degree of polysaccharide degradation and effectiveness of alcohol fermentation. The experiment was divided into two stages; in stage I, the possibility of obtaining fermentable sugars by hydrothermal and chemical treatment of the substrate was tested. Stage II involved an assessment of the effectiveness of the pretreatment methods to produce bioethanol in alcohol fermentation. Yeast used in industrial ethanol production—Saccharomyces cerevisiae As4—was used in the alcohol fermentation. The results have shown that the temperature of 150 °C was the most beneficial for the process of thermohydrolysis, and the mash in the microwave-heated sample contained the highest concentration of alcohol (0.97 g/l), which is 98% more than in the control mash and 37% more than in the conventionally heated sample.

Lignocellulosic biomass is a sustainable feedstock for fuel ethanol production, but it is characterized by low mass and energy densities, and distributed production with relatively small scales is more suitable for cellulosic ethanol, which can better balance cost for the feedstock logistics. Lignocellulosic biomass is recalcitrant to degradation, and pretreatment is needed, but more efficient pretreatment technologies should be developed based on an in-depth understanding of its biosynthesis and regulation for engineering plant cell walls with less recalcitrance. Simultaneous saccharification and co-fermentation has been developed for cellulosic ethanol production, but the concept has been mistakenly defined, since the saccharification and co-fermentation are by no means simultaneous. Lignin is unreactive, which not only occupies reactor spaces during the enzymatic hydrolysis of the cellulose component and ethanol fermentation thereafter, but also requires extra mixing, making high solid loading difficult for lignocellulosic biomass and ethanol titers substantially compromised, which consequently increases energy consumption for ethanol distillation and stillage discharge, presenting another challenge for cellulosic ethanol production. Pentose sugars released from the hydrolysis of hemicelluloses are not fermentable with Saccharomyces cerevisiae used for ethanol production from sugar- and starch-based feedstocks, and engineering the brewing yeast and other ethanologenic species such as Zymomonas mobilis with pentose metabolism has been performed within the past decades. However strategies for the simultaneous co-fermentation of pentose and hexose sugars that have been pursued overwhelmingly for strain development might be modified for robust ethanol production. Finally, unit integration and system optimization are needed to maximize economic and environmental benefits for cellulosic ethanol production. In this article, we critically reviewed updated progress, and highlighted challenges and strategies for solutions.

The study outlines an economical biorefinery concept to evaluate the potential of three aquatic weeds Eichhornia crassipes, Lemna minor and Azolla microphylla for co-production of ethanol and methane. Four different scenarios were investigated viz., scenario A-hydrothermal treatment followed by anaerobic digestion and ethanol fermentation respectively (HT → AD → EF), scenario B- thermochemical treatment followed by anaerobic digestion and ethanol fermentation respectively (TC → AD → EF), scenario C- hydrothermal treatment followed by ethanol fermentation and anaerobic digestion respectively (HT → EF → AD) and scenario D- thermochemical treatment followed by ethanol fermentation and anaerobic digestion respectively (TC → EF → AD). Sequential hydrothermal treatment and anaerobic digestion (HT → AD) in scenario A enhanced the hemicellulose removal by 68.5–73.5% and simultaneously enriched the cellulose content by 41.2–54.5%. This contributed to highest ethanol yield (0.167–0.231 g/g biomass) in scenario A, which was found comparable to that obtained in scenario D, wherein harsh and expensive thermochemical pretreatment was employed. Besides that, relatively higher methane yield of 209–257 dm3/kg TOCR (Total organic carbon removal) obtained in scenario A as compared to other scenarios (67.5–238 dm3/kg TOCR) improved the overall energy efficiency of the studied concept. The energetic assessment showed lowest total energy output (859.6–1322.7 kwh) in scenario B and C as compared to other scenarios (1041.8–1583.9 kwh), thereby confirming their incompetence in coupled bioenergy production. This study, therefore presents an economically and energetically sustainable approach for pretreatment and bioenergy production that could help in overcoming the constraints hindering the commercialization of cellulosic ethanol. The study also opens up possibility for development of coupled aquatic weeds-based wastewater treatment and bioenergy production system for an efficient exploitation of the phytoremediation property of aquatic weeds.

Production of fuel ethanol is one of the possible ways to utilize crude glycerol, substantial amounts of which are produced by biodiesel industry. Earlier, we have described construction of the recombinant strains of methylotrophic thermotolerant yeast Ogataea polymorpha with simultaneous overexpression of the genes PDC1 and ADH1, which produced increased amounts of ethanol from glycerol. In this work, we have further improved these strains by overexpression of genes involved either in oxidative (through dihydroxyacetone) or phosphorylative (through glycerol-3-phosphate) pathway of glycerol catabolism, as well as heterologous gene coding for glycerol transporter FPS1 from Komagataella phaffii (formerly, Pichia pastoris). Obtained recombinant strains produced up to 10.7 g/L of ethanol (with ethanol productivity 30 mg/g of biomass/hr and yield 132 mg/g of consumed glycerol) from pure glycerol and up to 3.55 g/L of ethanol (with ethanol productivity 11.6 mg/g of biomass/hr and yield 72.3 mg/g of consumed glycerol) from crude glycerol as a carbon source, which is approximately 15 times more relative to that of the O. polymorpha wild-type strain and 2.2 more relative to the earlier constructed strain.

International audience; Yeast strains were isolated from sugar cane molasses (S1), dates (S2) and figs (S3) and the ethanol production was evaluated in batch condition. A comparison was made with the yeast Saccharomyces cerevisiae. The strains showed tolerant characteristics to stressful conditions like salinity and ethanol. The isolated strains produced ethanol; at 20 h of fermentation ethanol yields were 0.38-0.39 g.g-1 , and the productivities were almost 0.58 g.L-1. S. cerevisiae and S1 tolerated up to 14% (v/v) of ethanol; while interestingly the isolates S2 and S3 were highly tolerant, up to 20% (v/v) ethanol. Thus, S2 and S3 could serve as potential strains for ethanol fermentation, with 0.27 and 0.29 g.g-1 yield of ethanol in the presence of 1.37 mol.L-1 NaCl. These values were higher than the value obtained using the yeast of reference and S1 (0.16 g.g-1). Co-cultures of S2 and S3 enhanced the ethanol production, increasing the yield of ethanol by 12.5% compared with the single culture. The strains were identified as species S.cerevisiae, and S2 and S3 were very similar. For an application in the valorization of biomass such as green macro-algae, some assays were done on a synthetic model medium of hydrolysate of macro-algae and the strains S2 and S3 demonstrated excellent fermentative performances.

The aim of this work was to study ethanol fermentation properties of the robust mutant Candida glycerinogenes UG21 from non-detoxified lignocellulose hydrolysate. C. glycerinogenes UG21 with high tolerance to elevated temperature, acetic acid, and furfural was obtained and applied in lignocellulose-based ethanol production. C. glycerinogenes UG21 exhibited highly-efficient degradation ability to furfural. High levels of acetic acid and furfural inhibited cell growths and ethanol production of Saccharomyces cerevisiae ZWA46 and industrial Angel yeast but had a slight impact on biomass and ethanol titer of C. glycerinogenes UG21. Using non-detoxified sugarcane bagasse hydrolysate, C. glycerinogenes UG21 reached 1.24 g/L/h of ethanol productivity at 40 °C but ethanol production of S. cerevisiae ZWA46 and Angel yeast was inhibited. Further, C. glycerinogenes UG-21 exhibited 2.42-fold and 1.58-fold higher productivity than S. cerevisiae ZWA46 and Angel yeast under low-toxicity hydrolysate. Therefore, C. glycerinogenes UG-21 could be an excellent candidate for low-cost lignocelluloses ethanol production.

White-rot fungi are microorganisms capable of ethanol fermentation; however, the specific conditions activating ethanol fermentation are unclear in contrast to fermentation by yeasts. In this study, we investigated the conditions favoring ethanol fermentation by the white-rot fungus Phanerochaete sordida YK-624, which is able to produce ethanol from woody material. In aerobic stationary cultivation with various concentrations of glucose (0.8-33 g/l), the fungus produced ethanol in media containing an initial glucose concentration of 2.8 g/l or higher. The amount of glucose consumption, mycelial weight, and ethanol production on the second day of culture increased in a concentration-dependent manner at low glucose concentrations; however, these were saturated at high concentrations. Biomass yields (growth/glucose consumption) were decreased until the initial glucose concentration increased to 6.0 g/l, after which the biomass yields showed constant values at higher concentrations (12-33 g/l). On the other hand, ethanol yields increased with decreasing biomass yields. In short shaking cultivation using mycelial suspension, trace amounts of instantaneous aerobic ethanol production were observed with 1.1 and 2.1 g/l glucose, but the relative gene expression levels of key enzymes at the pyruvate branch point showed no significant differences between ethanol production and non-production conditions. From these experimental results, it appears that the white-rot fungus P. sordida YK-624 produces ethanol due to overflow in sugar metabolism under aerobic conditions, although P. sordida YK-624 prioritizes glucose utilization for respiratory growth.

Full feedstock potential needs to be tapped to make lignocellulosic ethanol an economically viable reality. This work focuses on the Saccharomyces cerevisiae ethanol fermentation of fresh sorghum carbohydrates extracted through a mild steam-treatment process, and the subsequent Chlorella vulgaris cultivation using the generated liquid and gaseous fermentation effluents. The first section of the manuscript focuses on the effect of nutrient addition (fermentation effluent, yeast extract and urea) on the conversion efficiency of the sorghum carbohydrates to ethanol. Overall, the fermentation time was reduced to half when yeast extract and urea were supplemented to the free and hemicellulosic carbohydrate stream, accelerating the total sugar consumption time from 24 h to under 12 h. However, regarding the cellulosic carbohydrate hydrolysate, the sole addition of urea resulted in a slight improvement of the fermentation kinetics. The second half of the manuscript presents the impact of these different fermentation effluents and various process parameters (addition of yeast extract, antibiotic and CO2) on the microalgal cultivation and composition. The cellulosic hydrolysate yielded the highest concentrations of microalgal carbohydrates (507 mg/L) under a CO2-rich environment. Further cultivation scale-up assays confirmed these observations in the presence of 10% CO2 using the mixed fermentation effluents of the free and constitutive sorghum carbohydrates. Thus, an integrated sorghum-based first- (free carbohydrates), second- (constitutive carbohydrates) and third-generation (microalgal carbohydrates) ethanol production process was thoroughly investigated. This work could represent a step towards bridging the gap leading to full-scale commercialization of these advanced-biofuel technologies.

Low-world oil prices but supportive government policies provide growing environmental and energy security support favorable for the bioethanol market. The need to generate large and sustainable supply of biomass to make bioethanol will require the development of crops grown specifically for bioenergy production. Given the existing history of genetic improvement and infrastructure available for sorghum, (Sorghum bicolor L. Moench) hybrids will be one of the several species dedicated as energy crop and the subject of this study. Texas A & M University Sorghum Breeding Program has developed hybrid sorghum varieties with high protein digestibility and improved starch digestibility. Most of the previous research on grain sorghum focused on the digestibility of sorghum protein from the nutritional point of view. The aim of the current study was to select best sorghum lines from relatively large and diverse sorghum samples that breeders are currently working with for the development of new low energy input liquefaction, saccharification and fermentation methodologies to produce bioethanol. Limited researches studies report on the performance of sorghum varieties in ethanol fermentation in relation to the protein and starch digestibility of sorghum.

This work makes use of the so-called phenomenological non-structured modelling approach to propose a novel mathematical structure for the description and prediction of the pH effect over an Isopropanol-Butanol-Ethanol (IBE) fermentation system by Clostridium acetobutylicum pIPA3-Cm2, which includes both an in-line approximation of the pH of the culture medium and also novel expressions to reflect its real time effect over the biomass growth and metabolic response in an attempt to generate a base for the development of process intensification strategies for said fermentation system for biofuel production purposes. The proposed model attained a correlation index R2 = 0.9931 and a p-value

A novel biomass pretreatment method, i.e. pressurized microwave hydrothermal treatment with inorganic salts, and the simultaneous saccharification and fermentation (SSF) using salt-tolerant cellulase, i.e. Meicelase, and salt-tolerant yeast, i.e. Saccharomyces cerevisiae BA11, were studied for the efficient ethanol production from sugarcane bagasse. The component analysis, enzymatic saccharification, and alcohol fermentation were carried out using pressurized microwave treated sugarcane bagasse with various inorganic salts. The pressurized microwave treatment using 2 wt% MgCl2 at a treatment temperature of 200 °C for a treatment time of 5 min followed by SSF without washing treatment of inorganic salts provided the maximum glucose and ethanol yields, i.e. 0.392 and 0.18 g/g-raw material, those corresponded to 99 and 90% of saccharification and ethanol conversion ratios, respectively.

Background Large-scale processing of lignocellulosics for glucose production generally relies on high temperature and acidic or alkaline conditions. However, extreme conditions produce chemical contaminants that complicate downstream processing. A method that mainly rely on mechanical and enzymatic reaction completely averts such problem and generates unmodified lignin. Products from this process could find novel applications in the chemicals, feed and food industry. But a large-scale system suitable for this purpose is yet to be developed. In this study we applied simultaneous enzymatic saccharification and communition (SESC) for the pre-treatment of a representative lignocellulosic biomass, cedar softwood, under both laboratory and large-scale conditions. Results Laboratory-scale comminution achieved a maximum saccharification efficiency of 80% at the optimum pH of 6. It was possible to recycle the supernatant to concentrate the glucose without affecting the efficiency. During the direct alcohol fermentation of SESC slurry, a high yield of ethanol was attained. The mild reaction conditions prevented the generation of undesired chemical inhibitors. Large-scale SESC treatment using a commercial beads mill system achieved a saccharification efficiency of 60% at an energy consumption of 50 MJ/kg biomass. Conclusion SESC is very promising for the mild and clean processing of lignocellulose to generate glucose and unmodified lignin in a large scale. Economic feasibility is highly dependent on its potential to generate high value natural products for energy, specialty chemicals, feed and food application.

Background: Ensiling cannot be utilized as a stand-alone pretreatment for sugar-based biorefinery processes but, in combination with hydrothermal processing, it can enhance pretreatment while ensuring a stable long-term storage option for abundant but moist biomass. The effectiveness of combining ensiling with hydrothermal pretreatment depends on biomass nature, pretreatment, and silage conditions.Results: In the present study, the efficiency of the combined pretreatment was assessed by enzymatic hydrolysis and ethanol fermentation, and it was demonstrated that ensiling of sugarcane bagasse produces organic acids that can partly degrade biomass structure when in combination with hydrothermal treatment, with the consequent improvement of the enzymatic hydrolysis of cellulose and of the overall 2G bioethanol process efficiency. The optimal pretreatment conditions found in this study were those using ensiling and/or hydrothermal pretreatment at 190 °C for 10 min as this yielded the highest overall glucose recovery yield and ethanol yield from the raw material (0.28–0.30 g/g and 0.14 g/g, respectively).Conclusion: Ensiling prior to hydrothermal pretreatment offers a controlled solution for wet storage and long-term preservation for sugarcane bagasse, thus avoiding the need for drying. This preservation method combined with long-term storage practice can be an attractive option for integrated 1G/2G bioethanol plants, as it does not require large capital investments or energy inputs and leads to comparable or higher overall sugar recovery and ethanol yields.

Turion is a kind of dormant tissue from Spirodela polyrrhiza (L) Schleid and represents another duckweed-based starch production system, which owns several potential technical merits than the conventional one. This paper systematically investigated the physiological, biochemical and production characteristics of turion and preliminarily evaluate its feasibility for bioethanol production. Turion productivity of 3.78 g/m2/d and starch productivity of 2.90 g/m2/d was achieved in strain 0196. Full-component analysis revealed that turion is high-quality substrate as it contained high starch content (65.63%) and low lignocellulose content (12.82%). Besides, turion can be continuously produced by strain 0196 up to 6 weeks, indicating a sustainable manufacture of them is possible. Finally, harvested turion was used for ethanol fermentation for the first time with an ethanol yield of 0.34 g g−1(turion), resulted in an annual yield of 4.69 t/ha. This research elucidated that turion from duckweed is a novel biomass for biofuel production.

Microbial bio-alcohol production is achieved by fermentation mainly using carbohydrates as substrates, which are major components of biomass. Various types of microorganisms have the capacity to produce bio-alcohol and/or bio-hydrogen, however, for this chapter only hyperthermophiles will be discussed. Dependency and rapid consumption of fossil fuels result in significantly negative impacts on the environment. To combat such deteriorating trends and maintain sustainability, biofuels are rapidly considered to be a major alternative source of fuel. A biological or chemical process is needed to convert biomass into simple sugars that can be fermented by a particular microorganism. Depending on the microorganism, the type of alcohol fermentation can vary. Microbial hydrogen production has been found to be mainly from dark fermentation using complex biomass. Although they possess the metabolic pathways required for alcohol production, the yields are still quite low in comparison to other non-hyperthermophilic alcohol producing microorganisms.

Biofuels produced from photosynthetic microorganisms such as microalgae and cyanobacteria could potentially replace fossil fuels as they offer several advantages over fuels produced from lignocellulosic biomass. In this study, energy production potential in the form of bioethanol was examined using different biomasses derived from the growth of a cyanobacteria-based microbial consortium on a chemical medium and on agro-industrial wastewaters (i.e., dairy wastewater, winery wastewater and mixed winery–raisin effluent) supplemented with a raisin residue extract. The possibility of recovering fermentable sugars from a microbial biomass dominated by the filamentous cyanobacterium Leptolynbgya sp. was demonstrated. Of the different acid hydrolysis conditions tested, the best results were obtained with sulfuric acid 2.5 N for 120 min using dried biomass from dairy wastewater and mixed winery–raisin wastewaters. After optimizing sugar release from the microbial biomass by applying acid hydrolysis, alcoholic fermentation was performed using the yeast Saccharomyces cerevisiae. Raisin residue extract was added to the treated biomass broth in all experiments to enhance ethanol production. Results showed that up to 85.9% of the theoretical ethanol yield was achieved, indicating the potential use of cyanobacteria-based biomass in combination with a raisin residue extract as feedstock for bioethanol production.

Understanding the specific response of yeast cells to environmental stress factors is the starting point for selecting the conditions of adaptive culture in order to obtain a yeast line with increased resistance to a given stress factor. The aim of the study was to evaluate the specific cellular response of Saccharomyces cerevisiae strain Ethanol Red to stress caused by toxic by-products generated during the pretreatment of lignocellulose, such as levulinic acid, 5-hydroxymethylfurfural, furfural, ferulic acid, syringaldehyde and vanillin. The presence of 5-hydroxymethylfurfural at the highest analyzed concentration (5704.8 ± 249.3 mg/L) under aerobic conditions induced the overproduction of ergosterol and trehalose. On the other hand, under anaerobic conditions (during the alcoholic fermentation), a decrease in the biosynthesis of these environmental stress indicators was observed. The tested yeast strain was able to completely metabolize 5-hydroxymethylfurfural, furfural, syringaldehyde and vanillin, both under aerobic and anaerobic conditions. Yeast cells reacted to the presence of furan aldehydes by overproducing Hsp60 involved in the control of intracellular protein folding. The results may be helpful in optimizing the process parameters of second-generation ethanol production, in order to reduce the formation and toxic effects of fermentation inhibitors.

Made available in DSpace on 2021-06-25T11:10:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The efficiency of unpressurized ozonolysis (O) and acid washing (A) was investigated as a simple pretreatment procedure to depolymerize sugarcane biomass for posterior enzymatic hydrolysis and alcoholic fermentation to improve cellulosic ethanol production. The fiber chemical compositional analyses showed that the ozonolysis reduces the lignin content by 25%. High-performance anion-exchange chromatography (HPAEC-PAD) analysis showed that the loss of glucose during treatment was less than 1.5%. After enzymatic hydrolysis, the maximum glucose and xylose yield (310 ± 2 and 122 ± 3 mg g−1, respectively) were achieved from the OA treatment sequence and the fermentation yield was three times more ethanol than the yield from untreated bagasse. This simple treatment may be an alternative for improving cellulosic ethanol production using a mild-operational strategy. São Paulo State University (UNESP) Institute of Biosciences Humanities and Exact Sciences São Paulo State University (UNESP) Institute of Biosciences Humanities and Exact Sciences FAPESP: 2013/06234-3 FAPESP: 2015/11588-4