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With rapid growth of global population, meeting the increasing demand for food has become a significant challenge. This challenge is further compounded by limited arable land and the necessity to address the nutritional needs of both humans and animals. However, the utilization of straw biomass, which is readily available as an agricultural by‐product, presents a sustainable solution to this problem. Microbial fermentation has emerged as a highly effective method for converting non‐food biomass into protein, particularly known as single‐cell protein (SCP). Compared to traditional protein sources, SCP production through microbial fermentation is rapid and efficient, and requires minimal land resources. This review provides a comprehensive review of the research advancements in SCP from agricultural biomass, including pretreatment methods, microbial strains, and fermentation processes involved in the bioconversion of straw biomass. Due to the complexity of straw‐based biomass (SBB), it is essential to customize industrial strains and optimize the fermentation process to achieve the highest protein yield and productivity. Additionally, improving the compatibility between tailored processes and cost‐effective industrial strains can lead to the production of protein substitutes that are not only highly nutritious but also economically viable. Hence, the application of SCP derived from SBB presents a dual solution by reducing the need for managing agricultural residues and providing a sustainable source of protein. However, the production of SCP from SBB also has some limitations, such as protein‐synthesis efficiency, production cost, and difficulty to scale‐up the production process. In the future, there is great potential for significant advancements in the targeted conversion of SBB into protein by customizing high‐performance microbial strains. Several sensor and machine learning technologies will predict and monitor real‐time dynamic changes in the fermentation process of SBB, offering an opportunity to improve the production of sustainable SCP in an environmentally friendly and precise manner. [ABSTRACT FROM AUTHOR]

Sugarcane leaf waste, a byproduct of the growing global sugar industry, challenges agricultural waste management. This study explores its potential for methane production via anaerobic digestion. A microbial pre-hydrolysis, using lignocellulose-degrading bacteria, enhanced soluble chemical oxygen demand at an optimal initial substrate concentration of 40 g-volatile solid/L. Comparative analysis with untreated and bioaugmented leaves revealed the pre-hydrolyzed leaves achieved the highest methane production rate (MPR) at 14.0 ± 0.5 mL-CH4/L·d, surpassing others by 1.47 and 1.67 times. Two continuous stirred tank reactors were employed to assess the optimal hydraulic retention time (HRT). Results showed a stable methane production with an HRT of 25 days, yielding high MPRs: 88.70 ± 0.63 mL-CH4/L·d from pre-hydrolyzed sugarcane leaves and 82.57 ± 1.22 mL-CH4/L·d from microbial consortium-augmented leaves. A 25-day HRT fosters high microbial diversity with Bacteroidota, Firmicutes, Chloroflexi, and Verrucomicrobiota dominance, indicating favorable conditions. Conversely, a 20-day HRT results in lower diversity due to unfavorable factors like low pH during organic overloading, leading to increased concentrations of volatile fatty acids and lactic acid, with Firmicutes as the predominant phylum. This study highlights sugarcane leaf waste's potential as a valuable resource for sustainable methane production.

Lignin is considered by many as the ultimate barrier that impedes biomass conversion to fuels and chemicals. Several delignification strategies have been developed so far, but alkaline extraction remains the most widely used. However, this technology has a high chemical demand, consumes large amounts of water, and generates effluents that are hard to handle. Organosolv pulping is a good option for such application, but the impact of solvent losses and harmful emissions may be unsustainable. To this end, the use of greener alternatives such as water, biobased solvents, ionic liquids, and deep eutectic solvents, under sub- or supercritical conditions, may pave the road for the development of sustainable biorefineries.

Introduction: Fossil fuels are the main sources of water, soil, and air pollution that threaten human life and other organisms on Earth. Nowadays, the climate change and pollution are critical issues; however, many countries still use polluting fossil fuels. Therefore, finding alternative and clean fuels is a concern for many environmental activists and scientists. One of these alternative fuels is ethanol, which ignites cleaner due to its higher hydroxyl groups and lack of sulfur and nitrogen in its formula. Ethanol can be produced both chemically and biologically. Till now, four generations of bioethanol have been introduced. In the second generation, lignocellulosic materials are used as the main source for bioethanol production. These materials are frequently found in plant biomasses and agricultural residues, which are inexpensive and environmentally sustainable. Therefore, it is of importance to improve the production process and find novel techniques that increase final yields and process efficacy. In this study, the structural properties of lignocellulosic materials, pretreatment techniques, the second-generation bioethanol production process, and the effective bacterial and fungal strains in this procedure are investigated.Materials and Methods: This review study is a narrative review in which a logical search approach was selected. For data analysis, a comparative approach between the different methods was expressed in each section.Results: Among four bioethanol generations, the second generation has received remarkable attention due to its non-competition with human food and its industrial potential rather than other generations. Therefore, it is of particular significance to improve the production process of bioethanol second generation. A deep understanding of lignocellulosic components, pretreatment methods optimization, and increasing hydrolysis and fermentation processes efficiency make bioethanol production industrially possible and cost-effective.Discussion and Conclusion: However, despite extensive studies to select the most suitable microorganisms during the fermentation stage, Saccharomyces cerevisiae and Zymomonas mobilis are still at the forefront of studies.

Introduction: Fossil fuels are the main sources of water, soil, and air pollution that threaten human life and other organisms on Earth. Nowadays, the climate change and pollution are critical issues; however, many countries still use polluting fossil fuels. Therefore, finding alternative and clean fuels is a concern for many environmental activists and scientists. One of these alternative fuels is ethanol, which ignites cleaner due to its higher hydroxyl groups and lack of sulfur and nitrogen in its formula. Ethanol can be produced both chemically and biologically. Till now, four generations of bioethanol have been introduced. In the second generation, lignocellulosic materials are used as the main source for bioethanol production. These materials are frequently found in plant biomasses and agricultural residues, which are inexpensive and environmentally sustainable. Therefore, it is of importance to improve the production process and find novel techniques that increase final yields and process efficacy. In this study, the structural properties of lignocellulosic materials, pretreatment techniques, the second-generation bioethanol production process, and the effective bacterial and fungal strains in this procedure are investigated. Materials and Methods: This review study is a narrative review in which a logical search approach was selected. For data analysis, a comparative approach between the different methods was expressed in each section. Results: Among four bioethanol generations, the second generation has received remarkable attention due to its non-competition with human food and its industrial potential rather than other generations. Therefore, it is of particular significance to improve the production process of bioethanol second generation. A deep understanding of lignocellulosic components, pretreatment methods optimization, and increasing hydrolysis and fermentation processes efficiency make bioethanol production industrially possible and cost-effective. Discussion and Conclusion: However, despite extensive studies to select the most suitable microorganisms during the fermentation stage, Saccharomyces cerevisiae and Zymomonas mobilis are still at the forefront of studies. [ABSTRACT FROM AUTHOR]

After acidic and high-temperature pretreatment of lignocellulosic biomass, researchers find that some lignin-like substance appeared on the surface of cellulose, which is called pseudo-lignin. Pseudo-lignin can be formed through carbohydrate degradation or substitution reactions on the aromatic ring of lignin. Pseudo-lignin is identified as Klason lignin in compositional analysis, whereas in Py-GC-MS analysis, it is recognized as material derived from carbohydrates. Pseudo-lignin is an aromatic substance. Similar to lignin, it also affects enzymatic hydrolysis efficiency by blocking the enzymatic reaction sites of cellulose and non-productive adsorption with cellulases. In order to offer theoretical guidance and technical support for the advancement of cost-effective and efficient new pretreatment technology, this review summarizes the latest advancements in research concerning the origins of pseudo-lignin, its effects on enzymatic hydrolysis, and the strategies that inhibit pseudo-lignin formation. • Different pretreatment methods that result in the formation of pseudo-lignin are reviewed. • The specific mechanism of pseudo-lignin formation is clarified. • The deposition of pseudo-lignin inhibits enzymatic hydrolysis. • Measures to hinder the formation of pseudo-lignin are discussed. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) of animal manure converts only half of the organic material into biogas due to the presence of a significant amount of lignocellulosic materials in manure. In this study, alkaline thermal pretreatment was used for improving anaerobic digestion of residual manure fibers after AD. Anaerobic digestion of pretreated manure fibers was done in batch culture under mesophilic and thermophilic conditions. The results of the study showed that degradation of manure fibers was improved ca. 43.6% as a result of alkaline thermal pretreatment with 3% w/w NaOH added. Methane yield improved by 143.5 and 180.2% under mesophilic and thermophilic conditions, respectively. Compositional analysis of the effluent after AD showed the percentile conversion of 50.8% of cellulose, 59.5% of hemicellulose, 39.9% of acid-soluble and 21.7% of acid-insoluble lignin to methane under mesophilic conditions. Under thermophilic conditions, 57.3% of cellulose, 70.1% of hemicellulose, 39.4% of acid-soluble and 19.4% of acid-insoluble lignin were converted to methane. The result showed that alkaline thermal pretreatment of manure fibers can enhance the performance of AD while shortening the time needed to recover the maximum amount of biogas from AD. [ABSTRACT FROM AUTHOR]

Abstract The implementation of biorefineries based on lignocellulosic materials as an alternative to fossil-based refineries calls for efficient methods for fractionation and recovery of the products. The focus for the biorefinery concept for utilisation of biomass has shifted, from design of more or less energy-driven biorefineries, to much more versatile facilities where chemicals and energy carriers can be produced. The sugar-based biorefinery platform requires pretreatment of lignocellulosic materials, which can be very recalcitrant, to improve further processing through enzymatic hydrolysis, and for other downstream unit operations. This review summarises the development in the field of pretreatment (and to some extent, of fractionation) of various lignocellulosic materials. The number of publications indicates that biomass pretreatment plays a very important role for the biorefinery concept to be realised in full scale. The traditional pretreatment methods, for example, steam pretreatment (explosion), organosolv and hydrothermal treatment are covered in the review. In addition, the rapidly increasing interest for chemical treatment employing ionic liquids and deep-eutectic solvents are discussed and reviewed. It can be concluded that the huge variation of lignocellulosic materials makes it difficult to find a general process design for a biorefinery. Therefore, it is difficult to define “the best pretreatment” method. In the end, this depends on the proposed application, and any recommendation of a suitable pretreatment method must be based on a thorough techno-economic evaluation.

Dielectric Barrier Discharge (DBD) can be used to produce a large volume of non-thermal plasma at atmospheric pressure. Such plasmas are sources of highly reactive species (radicals, ozone, atoms, ions and excited molecules). Due to its characteristics, the DBD plasma can be applied for the pretreatment of lignocellulosic materials, in order to extract lignin that prevents the access to remained fermentable sugars in the biomass. In this context, an alternative method for pretreatment of lignocellulosic material in an in-liquid DBD plasma reactor using non-contact electrodes, working with atmospheric air, has been proposed. After the pretreatment, the solids were washed and submitted to enzymatic hydrolysis with a commercial enzyme complex, at 10 FPU/g of pretreated biomass and 50 g/L solids concentration (dry basis), for 72 h. The release of fermentable sugars was measured, comparing the samples obtained with and without plasma treatment. The highest sugar release was achieved using the plasma-in-liquid pretreatment in a single step, with glucose and xylose yields of 51.3 and 38.5%, respectively, after enzymatic hydrolysis. Thus, an effective pretreatment was developed to be applied to biomass such as: corn cob, sugarcane bagasse, bamboo, eucalyptus, etc., in order to reduce the environmental impact and, at the same time, produce biofuels. [ABSTRACT FROM AUTHOR]

The implementation of biorefineries based on lignocellulosic materials as an alternative to fossil-based refineries calls for efficient methods for fractionation and recovery of the products. The focus for the biorefinery concept for utilisation of biomass has shifted, from design of more or less energy-driven biorefineries, to much more versatile facilities where chemicals and energy carriers can be produced. The sugar-based biorefinery platform requires pretreatment of lignocellulosic materials, which can be very recalcitrant, to improve further processing through enzymatic hydrolysis, and for other downstream unit operations. This review summarises the development in the field of pretreatment (and to some extent, of fractionation) of various lignocellulosic materials. The number of publications indicates that biomass pretreatment plays a very important role for the biorefinery concept to be realised in full scale. The traditional pretreatment methods, for example, steam pretreatment (explosion), organosolv and hydrothermal treatment are covered in the review. In addition, the rapidly increasing interest for chemical treatment employing ionic liquids and deep-eutectic solvents are discussed and reviewed. It can be concluded that the huge variation of lignocellulosic materials makes it difficult to find a general process design for a biorefinery. Therefore, it is difficult to define "the best pretreatment" method. In the end, this depends on the proposed application, and any recommendation of a suitable pretreatment method must be based on a thorough techno-economic evaluation. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass resources are renewable materials that can be converted to fermentable sugars and subsequently into ethanol. Water hyacinth (Eichhornia crassipes) is a cellulosic aquatic plant that has high carbohydrates, low lignin content, and notable reducing sugars content in its structure. Based on the literature review in the case of water hyacinth, the most frequently used pretreatment methods were acid and alkali, while ionic liquid and microwave-assisted methods were used rarely. The dominant sugars were glucose, xylose, galactose, arabinose, and mannose. Based on the findings, cellulase and S. cerevisiae were mostly used for enzymatic hydrolysis and fermentation of water hyacinth to ethanol, respectively. This review presents the recent studies in pretreatment, hydrolysis, and fermentation of water hyacinth biomass into ethanol.

In this study, a series of ionic liquids including conventional, protic and Brønsted acidic-type ionic liquids were evaluated as media for the pretreatment of Taiwan grass. The pretreatments were carried out in parallel format, for the first time, in a novel glass reactor known as Q-tube. Based on the results, the Q-tube was very efficient for the pretreatment of our lignocellulosic materials in comparison with the conventional equipment (round bottom flask). Pretreatments were completed in one hour with high yield of reducing and total sugars after enzymatic hydrolysis. Some protic and Brønsted acidic ionic liquids can depolymerize partially the cellulosic material in one step and after enzymatic hydrolysis the content of reducing sugars is up to 35 times higher in comparison with the material without pretreatment. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass resources are renewable materials that can be converted to fermentable sugars and subsequently into ethanol. Water hyacinth (Eichhornia crassipes) is a cellulosic aquatic plant that has high carbohydrates, low lignin content, and notable reducing sugars content in its structure. Based on the literature review in the case of water hyacinth, the most frequently used pretreatment methods were acid and alkali, while ionic liquid and microwave-assisted methods were used rarely. The dominant sugars were glucose, xylose, galactose, arabinose, and mannose. Based on the findings, cellulase and S. cerevisiae were mostly used for enzymatic hydrolysis and fermentation of water hyacinth to ethanol, respectively. This review presents the recent studies in pretreatment, hydrolysis, and fermentation of water hyacinth biomass into ethanol. [ABSTRACT FROM AUTHOR]

This study attempted to enhance anaerobic conversion of lignocellulosic materials in excess sludge by bioaugmentation and pretreatment. The results reveal that highly active lignocellulolytic microorganisms ( Clostridium stercorarium and Bacteroides cellulosolvens ) could be enriched from anaerobic sludge in ordinarily operated anaerobic digester (AD). Inoculating these microorganisms into AD could substantially enhance the degradation of cellulose and hemicellulose. However, this effect of bioaugmentation was shielded for raw excess sludge due to lignin incrustation in native biosolids. For this problem, pretreatments including acid, alkali, thermal and ultrasonic methods were effectively used to deconstruct the lignin incrustation, in which thermal pretreatment was demonstrated to be the most effective one. Then, pretreatment associated with bioaugmentation was successfully used to enhance the energy conversion of lignocellulosic materials, which resulted in the degradation of cellulose, hemicellulose and lignin to 68.8–78.2%, 77.4–89% and 15.4–33.7% respectively and thus increased the CH 4 production by 210–246%, compared with ordinary AD. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of microwave (MW) and microwave–chemical (MWC) pretreatment on barley straw and to identify the acidic, basic, or oxidative chemicals that provide the highest sugar conversion for subsequent enzymatic hydrolysis. The MW and MWC processes were applied as a pretreatment step before fermentation. MW radiation at 200 and 300 W and MW radiation plus a chemical (H2SO4or NaOH or H2O2) as catalyst were applied, and total sugar, total phenol, and Klason and acid-soluble lignin were measured. Although the MWC pretreatment produced a higher total sugar concentration than the MW pretreatment, the addition of an NaOH solution produced the best results in terms of all parameters. Fourier transform infrared analysis was also performed to observe the deterioration of molecular structures after the application of MW and MWC. [ABSTRACT FROM PUBLISHER]

ABSTRACT In this study, we extend imaging and modeling work that was done in Part I of this report for a pure cellulose substrate (filter paper) to more industrially relevant substrates (untreated and pretreated hardwood and switchgrass). Using confocal fluorescence microscopy, we are able to track both the structure of the biomass particle via its autofluorescence, and bound enzyme from a commercial cellulase cocktail supplemented with a small fraction of fluorescently labeled Trichoderma reseii Cel7A. Imaging was performed throughout hydrolysis at temperatures relevant to industrial processing (50°C). Enzyme bound predominantly to areas with low autofluorescence, where structure loss and lignin removal had occurred during pretreatment; this confirms the importance of these processes for successful hydrolysis. The overall shape of both untreated and pretreated hardwood and switchgrass particles showed little change during enzymatic hydrolysis beyond a drop in autofluorescence intensity. The permanence of shape along with a relatively constant bound enzyme signal throughout hydrolysis was similar to observations previously made for filter paper, and was consistent with a modeling geometry of a hollowing out cylinder with widening pores represented as infinite slits. Modeling estimates of available surface areas for pretreated biomass were consistent with previously reported experimental results. Biotechnol. Bioeng. 2015;112: 32-42. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT Enzymatic hydrolysis is one of the critical steps in depolymerizing lignocellulosic biomass into fermentable sugars for further upgrading into fuels and/or chemicals. However, many studies still rely on empirical trends to optimize enzymatic reactions. An improved understanding of enzymatic hydrolysis could allow research efforts to follow a rational design guided by an appropriate theoretical framework. In this study, we present a method to image cellulosic substrates with complex three-dimensional structure, such as filter paper, undergoing hydrolysis under conditions relevant to industrial saccharification processes (i.e., temperature of 50°C, using commercial cellulolytic cocktails). Fluorescence intensities resulting from confocal images were used to estimate parameters for a diffusion and reaction model. Furthermore, the observation of a relatively constant bound enzyme fluorescence signal throughout hydrolysis supported our modeling assumption regarding the structure of biomass during hydrolysis. The observed behavior suggests that pore evolution can be modeled as widening of infinitely long slits. The resulting model accurately predicts the concentrations of soluble carbohydrates obtained from independent saccharification experiments conducted in bulk, demonstrating its relevance to biomass conversion work. Biotechnol. Bioeng. 2015;112: 21-31. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: In this work, dilute sulphuric acid prehydrolysis of residual empty pods of Moringa oleifera fruits was investigated as pretreatment for enzymatic hydrolysis of cellulose. In experiments performed at 130–190°C for 10–30min, corresponding to a severity range between log R o =1.9 and log R o =4.2, the effect of pretreatment conditions on the recovery of polysaccharides and on the enzymatic convertibility of cellulose was evaluated. Overall cellulose recovery was above 95% in the pretreatments performed at 130 and 160°C, and between 87 and 90% in the pretreatments at 190°C, while xylan recovery in the most severe pretreatments was only 24.7–50.2%. The highest sugar concentration in the acid prehydrolysates (15.0g/L) was obtained in the pretreatment performed at 160°C and 20min. The formation of degradation products was low at mild pretreatment conditions, but it increased with the severity. Furfural concentration reached 4.04g/L at log R o =3.1 and decreased again with a further increase of the pretreatment severity. HMF, formic acid and levulinic acid were formed only in the most severe pretreatments. The pretreatment was effective for improving the enzymatic hydrolysis of cellulose, and the highest conversion (84.3%) was achieved in the material pretreated at mid severity (log R o =3.1). [Copyright &y& Elsevier]

Rice hulls are potential low-cost feedstocks for fuel ethanol production in many countries. Most of the relevant publications are devoted to homogenous (high quality) hulls generated in industrial mills. On the other hand, small-scale mills give rise to hulls containing grain fragments and bran. In the present work, the dilute-acid pretreatment of such heterogeneous rice hulls was investigated based on a central composite rotatable experimental design. The variables were: temperature (140-210°C), biomass load (5-20%), and sulfuric acid concentration (0.5-1.5% based on reaction mixture). A total of 16 experimental runs were carried out, including a 23-plan, two replicates at the central point and six star points. Low temperatures were found to be favorable for the hydrolysis of xylan and of the easily hydrolyzable glucan fraction. High glucose formation (up to 15.3% of the raw material dry weight), attributable to starch hydrolysis, was detected in the hydrolysates obtained under the least severe pretreatment conditions. Several models were developed for predicting the effect of the operational conditions on the yield of pretreated solids, xylan and glucan conversion upon pretreatment, and on enzymatic convertibility of cellulose. The pretreatment temperature exerted the most significant effect on the conversion of the polysaccharides. Optimum results were predicted for the conversion of easily-hydrolyzable glucan in the material pretreated at 140.7°C, and for the enzymatic saccharification of cellulose in the material pretreated at 169°C. These results are interpreted that a two-step acid hydrolysis may be the best pretreatment strategy for heterogeneous rice hulls produced in small mills. [ABSTRACT FROM AUTHOR]

The electro-assisted organosolv pretreatment (EAOP) is a biomass pretreatment method which is viable at room temperature. Previously, it was shown that the electrochemically generated hydroxyl radical (OH*) during EAOP is key to the delignification efficiency when 1-butyl-3-methylimidazolium acetate and gamma-valerolactone (10 wt% [Bmim]OAc/GVL) are used as the solvent. However, the effect of additives and biomass loading on this novel pretreatment process have not previously been investigated. In this study, inorganic salts of NaOH, NaCl, FeCl 3 , with and without added water, were used as additives into [Bmim]OAc/GVL, to determine their effect on OH* formation during EAOP. These inorganic salts were selected as they have been proven effective in the electrochemical conversion of either lignin or cellulose. It was found that [Bmim]OAc/GVL with NaCl/water showed the most rapid and largest amount of OH* formation, being 45% higher than [Bmim]OAc/GVL without additives. The 240-min EAOP with NaCl/water delignified 70.8 wt% of Eucalyptus sawdust and the residual biomass showed 204.4 mg/g total reducing sugar yield. In addition, EAOP with NaCl/water present can be done rapidly (in 30 min) and at high biomass loading (25%). The total reducing sugar (TRS) yield of sawdust from the high-loading rapid EAOP is up to 194.0 mg/g, which is around 10-fold higher than untreated sawdust. The spent solvent from EAOP could be regenerated, with only minor TRS yield decrease (10%) observed after recycling the solvent four times. NaCl and water were added into the electro-assisted organosolv pretreatment as inorganic additives, which enabled EAOP to be completed in 30 min at 25% biomass loading. The residual biomass from EAOP can produce up to 204.4 mg/g reducing sugar (approximately 10-folds higher than untreated biomass) and the regenerated solvent showed only minor decreases (10%) in total reducing sugar yield after four cycles. [Display omitted] • Electro-assisted organosolv pretreatment (EAOP) and different inorganic additives. • Addition of NaCl/water increased the OH* generation by 45% during EAOP • Optimum EAOP fractionation with NaCl/water for 30 min at 25% biomass loading. • RB after EAOP produced reducing sugar 10-folds higher than untreated biomass. • Only 10% decrease in the TRS yield using regenerated solvent after four cycles. [ABSTRACT FROM AUTHOR]

Because of the recalcitrant nature of lignocellulosic materials, it is important to pretreat the biomass in order to obtain a suitable material for the bioconversion. In this study, two different types of pretreatments were performed. The first experiment used a 2-gal Parr reactor operated at 140, 150,160, and 170‡C with sulfuric acid concentrations varying from 0.5 to 2%. A second pretreatment was performed with a two-stage low-temperature process. The first-stage pretreatment was performed at 100 or 120‡C with sulfuric acid concentrations of 0.5, 2, and 5% followed by a secondstage pretreatment at 120‡C with 2% acid concentration. The best residues for enzymatic hydrolysis and simultaneous saccharification and fermentations (SSF) came from the higher temperature pretreatment with the Parr reactor. However, a large portion of the xylose fraction was degraded to furfural and glucose was degraded to HMF. On the contrary, the two-stage low temperature pretreatment resulted in a very low percentage of xylose degradation, and no glucose degradation. The residues from this two-stage pretreatment performed satisfactorily toward the production of ethanol by SSFs. This study discusses the results obtained from these experiments. [ABSTRACT FROM AUTHOR]