Method for efficient hydrolysis of lignocellulosic feedstocks in the presence of additives - Patent Application 20070122999

Abstract

A method for efficiently hydrolyzing lignocellulosic feedstocks in the presence of additives. The present disclosure relates to an improved method for enzymatically hydrolyzing a lignocellulosic feedstock, comprising the steps of impregnating a lignocellulosic feedstock to obtain an impregnated slurry, adjusting the concentration and pH of the treated slurry to obtain a stream, adding an additive to the stream to obtain an additive-treated stream, and enzymatically hydrolyzing the additive-treated stream to obtain an enzymatically hydrolyzed stream containing fermentable sugars. The present disclosure also discloses a step of co-fermenting the enzymatically hydrolyzed stream to obtain a fermentation product. The improved method for enzymatically hydrolyzing a lignocellulosic feedstock of the present invention is characterized in that the addition of an additive to the stream increases the efficiency of enzymatic hydrolysis by at least 7%.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Indian Patent Application No. 202221042375, filed on July 25, 2022.

[0003] The present invention relates to the production of biofuels from lignocellulosic feedstocks, and more particularly to the efficient enzymatic hydrolysis of lignocellulosic feedstocks, preferably softwood, in the presence of additives. [Background technology]

[0004] Ethanol, obtained from carbohydrates through fermentation, is one of the best alternatives for replacing traditional energy sources and reducing dependence on other fossil fuels. First-generation bioethanol is produced by enzymatic hydrolysis and fermentation of valuable food crops, but the depletion of food crops could lead to a food crisis. Therefore, there has been great interest in feedstock conversion systems that do not use food crops. Second-generation ethanol is produced sustainably using lignocellulosic feedstocks, including residual inedible parts of crops, such as stems, leaves, bagasse, and husks. To be competitive and gain acceptance of bioethanol on a commercial scale, biomass-to-ethanol conversion must be cost-effective.

[0005] Lignocellulosic feedstocks are abundant and primarily include agricultural residues, softwoods, forest residues, and hardwoods. Lignocellulosic feedstocks are primarily composed of three major polymers: cellulose (35-50%), hemicellulose (20-30%), and lignin (15-25%), which are intricately intertwined within the lignocellulosic structure. These can be hydrolyzed to produce simple sugars, most of which can be fermented.

[0006] However, obtaining high yields of monosaccharides derived from cellulose and hemicellulose from lignocellulosic feedstocks is more difficult than obtaining sugars from sugar- and starch-containing crops such as sugarcane and corn. Furthermore, the heterogeneity of feedstocks and the influence of various processing conditions on microorganisms and enzymes make the process of producing ethanol from lignocellulosic feedstocks more complicated.

[0007] Among lignocellulosic raw materials, softwood is a type of wood obtained from coniferous trees. Softwood is generally lighter and less dense than hardwood, and is known for its straight grain and uniform texture. Hardwoods and deciduous trees typically contain 38–49% cellulose, 23–30% lignin, and 19–26% pentosans. On the other hand, softwood is attractive because it has a high content of cellulose (40–45%) and lignin (26–34%) and a low content of pentosans (7–14%). The low pentosan content is advantageous because more aggressive processing conditions can be used to remove lignin without compromising the production of toxic inhibitors.

[0008] Although ethanol can be produced from softwood in a variety of ways, the general processing steps for producing ethanol from feedstocks typically consist of four steps: (1) pretreatment to increase the availability of lignocellulose, (2) enzymatic hydrolysis or saccharification to release fermentable sugars, (3) microbial fermentation to produce the desired product, and (4) purification of the fermentation broth by distillation.

[0009] Pretreatment involves breaking down the natural inert physical barriers, making more carbohydrates available for downstream hydrolysis processes. Generally, pretreatment methods involve chemical, physical, biological, or physicochemical steps that result in changes to the biomass structure.

[0010] After pretreatment, cellulose is hydrolyzed using cellulase. However, the dense structure of cellulose and hemicellulose, along with physical shielding by lignin, increases resistance to enzymatic action, leading to incomplete or low hydrolysis. Furthermore, lignin in softwood is known to adsorb to cellulolytic enzymes and inhibit their action, affecting yield and requiring more enzyme. Enzyme consumption is an important consideration in commercializing feedstock processing. Cellulase preparation requires expensive equipment and high operating costs, which can pose significant challenges in commercial downstream processing of the feedstock. Therefore, there is a need in the art to optimize and commercially viable methods for obtaining maximum yields of fermentable monosaccharides from lignocellulosic feedstocks, such as softwood.

[0011] Promising and important interfaces of enzyme accessibility and activity may include the application of additives such as surfactants, chelating agents, proteins, and synthetic polymers that can favorably influence the hydrolysis outcome. Their main mechanisms of action include (1) reducing non-productive enzyme adsorption, (2) increasing enzyme stability and activity and protecting them from denaturation due to heat and shear forces, (3) reducing the surface tension of lignocellulose and improving cellulose accessibility, and (4) facilitating enzyme recycling.

[0012] Therefore, the present application relates to the use of additives to improve the economics of pretreatment, increase the yield of the process, reduce the amount of enzyme required, and improve the enzymatic hydrolysis of softwood into simple sugars to obtain ethanol through a fermentation process. Summary of the Invention

[0013] This Summary is not intended to identify all essential features of the claimed subject matter, nor is it intended for use in determining or limiting the scope of the claimed subject matter. This Summary is provided to introduce concepts related to the use of additives to obtain ethanol through a fermentation process, concepts that are further described below in the Detailed Description of the Invention.

[0014] The presently disclosed subject matter is an improved method for enzymatically hydrolyzing a lignocellulosic feedstock, comprising the steps of impregnating a lignocellulosic feedstock to obtain an impregnation slurry; adjusting at least the concentration and pH of the impregnation slurry to obtain a stream; adding an additive to the stream to obtain an additive-treated stream; enzymatically hydrolyzing the additive-treated stream to obtain an enzymatically hydrolyzed stream comprising fermentable sugars; and fermenting the enzymatically hydrolyzed stream to obtain a fermentation product. The improved method for enzymatically hydrolyzing a lignocellulosic feedstock of the present invention is characterized in that the addition of an additive to the stream increases the efficiency of the enzymatic hydrolysis by at least 7%. [Brief explanation of the drawings]

[0015] The drawings are generally described with reference to the accompanying figures, in which the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears, and the same numbers are used throughout the figures to reference like features and components.

[0016] [Figure 1] FIG. 1 is a flow chart illustrating the enzymatic hydrolysis of lignocellulosic feedstocks using additives. Detailed Description of the Invention

[0017] Throughout this specification, references to "various embodiments," "some embodiments," "one embodiment," or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, appearances of the phrases "various embodiments," "some embodiments," "one embodiment," or "an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0018] Before describing the methods or steps of the present application, it should be understood that the present application is not limited to particular methods or organisms, as there may be multiple possible embodiments not expressly set forth herein that may still be operable within the scope of the present application.

[0019] Additionally, the technical solutions provided by the present disclosure are clearly and completely described below. Examples in which specific reagents or conditions may not be specified are carried out under conventional conditions or in the manner recommended by the manufacturer.

[0020] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All compositional values and ranges based on percentages are percent by weight unless otherwise indicated. All numerical or conditional ranges are meant to encompass any specific value included within the range, and are rounded to any appropriate decimal point.

[0021] In one embodiment, the presently disclosed subject matter provides an improved method for enzymatically hydrolyzing a lignocellulosic feedstock, comprising impregnating a lignocellulosic feedstock to obtain an impregnated slurry and adjusting the concentration and pH of the treated slurry to obtain a stream. The invention further discloses adding an additive to the stream to obtain an additive-treated stream, and enzymatically hydrolyzing the additive-treated stream to obtain an enzymatically hydrolyzed stream comprising fermentable sugars. The invention also discloses fermenting the enzymatically hydrolyzed stream to obtain a fermentation product, wherein the hydrolysis is carried out using active dry yeast. The improved method for enzymatically hydrolyzing a lignocellulosic feedstock of the invention is characterized in that adding an additive to the stream increases the efficiency of enzymatic hydrolysis by at least 7%.

[0022] In one embodiment of the present invention, the method includes several steps, each having one or more elements for performing a specific function required in an integrated process for obtaining ethanol and protein from grain. Those skilled in the art will recognize different variations and / or combinations of these elements that can be used to carry out the objectives of the invention disclosed herein.

[0023] As used herein, the term "lignocellulosic feedstock" refers to plant biomass containing cellulose (35-50%), hemicellulose (20-30%), and lignin (15-25%).

[0024] Some embodiments of the present invention relate to improved methods for the enzymatic hydrolysis of lignocellulosic feedstocks. Some embodiments of the present invention allow for the processing of lignocellulosic feedstocks such as annual grasses, energy crops, or other annually renewable feedstocks. In preferred embodiments, the lignocellulosic feedstock is selected from softwood, forest residues, or combinations thereof.

[0025] The term "softwood" as used herein refers to a type of wood derived from conifers and containing cellulose (40-45%), hemicellulose (15-25%), and lignin (26-34%). In this disclosure, softwood is the preferred lignocellulosic feedstock of choice for ethanol production. Softwood also has the potential to primarily produce monomeric hexoses, which are much easier to ferment than pentoses. Examples of softwood include pine, spruce, cedar, and fir.

[0026] Pre-processing of softwood is carried out to obtain a desired or predetermined particle size of the raw material. Pre-processing is optionally carried out using one or more techniques selected from crushing, size separation, and combinations thereof, depending on the physical form of the softwood. The term "pre-processing" includes size reduction prior to feeding to the digester.

[0027] Size reduction is a necessary preliminary step in pre-processing to obtain adequate yields in ethanol production from softwood, and has been shown to alter important physical and structural components of softwood, such as surface area to volume ratio, shape, number of interparticle bonds, and cellulose crystallinity.

[0028] In processes for converting softwood into various components, it is often desirable to impregnate the raw material with an impregnating agent prior to downstream processing. In this context, the term "impregnation" as used herein refers to the introduction of an impregnating agent into the raw material. In some cases, the impregnating agent may dissolve at least a portion of the softwood, thereby disrupting the robust structure and carbohydrate lignin matrix present in the raw material.

[0029] In certain embodiments, the impregnation step involves mixing the processed material or feedstock with water and an impregnation agent and adding it to an impregnation chamber using a screw feeder.

[0030] In a preferred embodiment, softwood is impregnated by mixing the processed raw material, or raw material, with at least one reactant selected from, but not limited to, an acid, a salt of an acid, a base, a salt of a base, or combinations thereof to obtain an impregnation slurry.

[0031] Impregnation of the processed feedstock, or raw material, with an impregnating agent to obtain an impregnation slurry is carried out by treatment with sulfuric acid, sulfurous acid, sulfur dioxide, nitric acid, phosphoric acid, hydrochloric acid, acetic acid, formic acid, maleic acid, lactic acid, and combinations thereof.

[0032] In a preferred embodiment, impregnation involves treating the processed feedstock with SO2 as an impregnation agent. SO2 (the impregnation agent) is used in gas or liquid form. The impregnation process can be carried out in any conventional manner using appropriate parameters / conditions known in the art to achieve the intended purpose.

[0033] As used herein, the terms "pretreatment" or "treatment" refer to physical and / or chemical treatments that render the cellulose component of a feedstock accessible to enzymes that convert the carbohydrate polymers to fermentable sugars in a subsequent enzymatic hydrolysis step and / or that render the physical structure of the feedstock susceptible to such enzymatic hydrolysis. Pretreatment conditions are selected appropriately to achieve the desired objective.

[0034] In some embodiments, the pretreatment is carried out at any suitable temperature, in one embodiment, at a temperature in the range of 100 to 250°C, preferably 150 to 240°C, and more preferably 180 to 220°C.

[0035] The pretreatment step can be carried out at any appropriate pressure. In one embodiment, the pretreatment is carried out at a pressure in the range of 0.5 MPa or more and 3.5 MPa or less, more preferably 0.75 MPa or more and 3 MPa or less, and more preferably 1.0 MPa or more and 2.5 MPa or less.

[0036] In a preferred embodiment, further treating the impregnated slurry comprises heating at a temperature in the range of 180°C to 210°C and a pressure of 1.5 to 1.8 MPa for 5 to 30 minutes to obtain a treated slurry.

[0037] The effectiveness of the treatment depends on a combination of factors such as the temperature, pressure, pH, and time to which the material is exposed. It is usually desirable to use the mildest possible combination of pretreatment conditions.

[0038] In one embodiment, the concentration and pH of the treated slurry are adjusted to obtain a stream. The impregnated slurry, which is further processed to obtain a treated slurry, comprises suspended solids and dissolved solids, the suspended solids further comprising cellulosic material. In another related embodiment, the concentration of the treated slurry is adjusted to about 15-25% w / w total solids by dilution with water or reclaimed water.

[0039] In one embodiment, the pH of the treatment slurry is adjusted to a range of 5.0 to 5.5 and maintained at a temperature in the range of 52 to 55°C.

[0040] The addition of additives to softwood during the pretreatment step prior to enzymatic hydrolysis has been shown to significantly improve the efficiency of the hydrolysis process, thereby increasing the sugar yield obtained by hydrolyzing the cellulose component of the feedstock.

[0041] The additive is believed to bind to lignin in the feedstock and prevent it from binding to the enzyme catalyst during hydrolysis, thereby increasing the amount of enzyme available for productive catalysis on the cellulosic substrate. The additive tends to remain bound during downstream processing after the pretreatment step, such as during subsequent washing of the biomass and subsequent hydrolysis.

[0042] In one embodiment, an additive is added to the stream to provide an additive-treated stream.

[0043] Many additives, including surfactants, proteins, and synthetic polymers, can enhance enzymatic hydrolysis by blocking nonproductive adsorption sites on lignin. Addition of surfactants such as Triton X-100 and Tween 20 at concentrations ranging from 0.03 to 0.3 g / L increased cellulose conversion rates by 9 to 21%, depending on the lignin content. Proteins such as BSA can also bind to lignin, preventing nonproductive binding by cellulase. Furthermore, synthetic polymers containing ethylene oxide, such as polyethylene glycol, polyol esters, polyoxyethylene esters, nonionic surfactants, such as poloxamers, and inorganic salts, such as K2CO3, K3PO4, K2HPO4, KH2PO4, K2SO4, and KCl, are also used as additives to enhance the efficiency of enzymatic hydrolysis.

[0044] The additives bind to the remaining lignin on the substrate through hydrophobic interactions, inhibiting the adsorption of cellulase to the lignin, and alter the surface properties of lignin, such as its hydrophobicity, hydrogen bonding ability, and surface charge.

[0045] In some embodiments, the additive is selected from polyhydroxy alcohols, glycols, nonionic surfactants, inorganic salts, and combinations thereof. In related embodiments, the additive is added at a rate ranging from 0.25 to 15.0% w / w of total solids at 50-55°C over a period of 5-60 minutes.

[0046] The process according to the invention comprises a subsequent step of enzymatic hydrolysis in which the additive-treated stream is subjected to enzymatic hydrolysis of one or more of its cellulosic components and converted into sugars.

[0047] In one embodiment, the additive-treated stream is treated with an enzyme to obtain an enzymatically hydrolyzed stream containing fermentable sugars.

[0048] In particular, enzymatic hydrolysis involves contacting the additive-treated stream with a mixture of cellulolytic enzymes, including, but not limited to, endoglucanases, exoglucanases, hemicellulases, and mixtures thereof.

[0049] In a specific embodiment of the present invention, the enzyme is used in a dosage of 0.1 to 25%, preferably 0.5 to 10%, more preferably 1 to 6%.

[0050] In another embodiment, the enzymatic hydrolysis is carried out at a temperature of 10 to 90°C, preferably 20 to 70°C, more preferably 40 to 60°C.

[0051] In a related embodiment, the enzymatic hydrolysis is carried out at a pH in the range of 2-7, preferably 3-7, more preferably 4-6.

[0052] The enzymatic hydrolysis step can be carried out for any suitable time, preferably 20 to 90 hours, more preferably 30 to 80 hours, and even more preferably 60 to 75 hours. In a preferred embodiment, the enzymatic hydrolysis is carried out with a cellulolytic enzyme mixture at a dosage ranging from 1 to 6%, at a pH ranging from 4.8 to 5.2, and at a temperature ranging from 50 to 55°C for 72 hours.

[0053] The enzymatic hydrolysis results in the production of one or more sugars, such as glucose, which can be advantageously used in a fermentation process to produce one or more alcohols.

[0054] In another embodiment, the enzymatically hydrolyzed stream comprises 4-8% glucose, 0.5-1.5% xylose, 0.2-0.5% galactose, and 2.0-3% mannose.

[0055] The fermentation of the enzymatically hydrolyzed stream can be carried out in any conventional manner. In one embodiment, the fermentation of the enzymatically hydrolyzed stream is carried out to obtain a fermentation product. In particular, the fermentation can be catalyzed by a microorganism, more particularly a yeast or a bacterium, such as a member of the genera Saccharomyces, Lactobacillus, Actinobacillus, Pichia, or Candida.

[0056] In one embodiment, the co-fermentation of the enzymatically hydrolyzed stream to obtain the fermentation product is carried out using whole cells (yeast or bacteria). In a preferred embodiment, the co-fermentation of the enzymatically hydrolyzed stream to obtain the fermentation product is carried out with active dry yeast.

[0057] The fermentation product may be any product resulting from fermentation, including ethanol, isopropanol, acetone, n-butanol, isobutanol, 1,4-butanediol, succinic acid, lactic acid, etc. In a preferred embodiment, the fermentation product comprises ethanol.

[0058] A method according to one embodiment of the present invention may include one or more additional processing steps after the fermentation step. For example, the method may include separating residues from the biomass or feedstock, particularly the fermentation broth, e.g., by centrifugation, and / or recovering desired fermentation products, e.g., by distillation, and / or purifying the recovered fermentation products. The fermentation product yield (e.g., ethanol yield) is the yield of the end product produced in the fermentation.

[0059] The terms "bioethanol" or "ethanol" are used interchangeably herein with "ethanol" and refer to ethanol produced from the conversion of plant matter.

[0060] According to one aspect, the present invention provides efficient enzymatic / enzyme-catalyzed hydrolysis of softwood in the presence of additives to produce fermentable sugars from softwood for one or more of the following purposes: i. Improving the efficiency of the process, or of the processing steps forming part of the process, in particular the hydrolysis of the cellulose component of softwood; and ii. Improving the yield of fermentable sugars

[0061] An improved yield of fermentable sugars may be manifested by a higher yield in any one or more fermentable sugars at a particular time point and / or over a particular period of time and / or upon completion of the method or hydrolysis step forming part of the method.

[0062] In a preferred embodiment, the improved method for the enzymatic hydrolysis of softwood is characterized by increasing the efficiency of the enzymatic hydrolysis by at least 7% by adding an additive to the stream.

[0063] Additionally, processes for obtaining fermentable sugars from softwood or other processes for the treatment of softwood that involve enzymatic hydrolysis of softwood can be marketed as benefiting from improvements, particularly greater efficiency, due to the use of additives in the process. [Example]

[0064] The following examples are included to provide illustration of the presently disclosed subject matter. Given this disclosure and general level of skill in the art, those skilled in the art will appreciate that the following examples are intended to be illustrative only, and that numerous changes, modifications, and variations can be adopted without departing from the spirit and scope of the presently disclosed subject matter.

[0065] Material Source: Norway spruce sawdust was used, obtained from Nordic countries. Cellulase enzymes were sourced from Novozymes. Active dry yeast was obtained from Leaf technologies, Chile.

[0066] Example 1: Enzymatic Hydrolysis of Softwood Softwood sawdust from Norway spruce (60 kg) and pine (60 kg) was used as lignocellulosic feedstock to investigate the effect of additives on enzymatic hydrolysis. Initial analysis of Norway spruce and pine revealed compositions including total solids, dissolved solids, lignin, ash, and protein (Table 1).

[0067] [Table 1]

[0068] The softwood was impregnated with SO2 (liquid or gaseous or a combination thereof) at an inlet flow rate of 60 kg / h delivering approximately 0.36 kg / h to obtain an impregnation slurry. Prior to impregnation, the softwood may optionally be pre-processed by a size reduction step to increase the impregnation efficiency.

[0069] The impregnated slurry was passed through a continuous pretreatment device at a temperature of 195°C and a pressure of 1.8 MPa for 10 minutes, yielding 130 kg / h of pretreated slurry in 1 hour.

[0070] Furthermore, 5.3 kg of the treated slurry at pH 1.5 was diluted with 1.7 kg of water to adjust the concentration of the slurry to a total solids content of 19.67% Norway spruce and 16.81% pine (Table 2). The pH was also increased from 1.5 to 5.5 by treatment with 81 g of aqueous ammonia to obtain a stream.

[0071] [Table 2]

[0072] Additives including PEG 1500, PEG 4000, Tween 80, Tween 20, and Triton X100 were used alone or in combination at 0.25–2% w / w with a 3% enzyme dosage (Cellic SE 1.0, enzyme activity 2343 BHU / g) maintained at 50–52°C and pH 5.0–5.2 for 72 h with continuous stirring at 300 rpm to obtain the additive-treated stream.

[0073] Varying the additives alone or in combination resulted in significant differences in enzyme efficiency ranging from 67.72% to 75.73%. Streams treated with Tween 80 at doses of 0.5-2% w / w showed the highest enzyme efficiency of 75.73% compared to the control (63.87%), followed by PEG 4000 at 74.20% (Table 3). The additives used alone proved more effective than the additives used in combination.

[0074] [Table 3]

[0075] The effect of varying enzyme dosage on enzymatic hydrolysis efficiency was measured using additive-treated streams of Norway spruce (18.18% w / w) and pine (16.8% w / w) total solids. The additive-treated streams were treated with 1.5–15% w / w (based on total solids) of a cellulolytic enzyme mixture (Cellic SE 1.0, enzyme activity 2343 BHU / g) at temperatures ranging from 45–55°C and pH ranging from 4.5–5.5 for approximately 72–120 hours to obtain the enzymatically hydrolyzed streams.

[0076] The percent conversion of glucan to glucose in enzymatic hydrolysis of enzymatically hydrolyzed streams increased as the enzyme dosage increased from 1.5% to 15%. An enzyme dosage of 15% w / w showed the highest conversion (Table 4). Streams enzymatically hydrolyzed with 15% PEG 4000 showed the highest glucan to glucose conversion rates of 86.10% and 86.5% for Norway spruce and pine, respectively.

[0077] [Table 4]

[0078] 0.7 kg of additive-treated, enzymatically hydrolyzed streams of Norway spruce and pine were treated with 1 kg / KL ethanol and active dry yeast containing 0.1% w / w urea at 32°C for 48 h to obtain an ethanol-rich fermentation broth.

Claims

1. 1. An improved method for enzymatic hydrolysis of lignocellulosic feedstock, comprising: impregnating the lignocellulosic raw material to obtain an impregnation slurry; adjusting at least the concentration and pH of the impregnation slurry to obtain a stream; adding an additive to said stream to obtain an additive-treated stream; enzymatically hydrolyzing the additive-treated stream to obtain an enzymatically hydrolyzed stream comprising fermentable sugars; and fermenting the enzymatically hydrolyzed stream to obtain a fermentation product. The method of claim 1, wherein adding an additive to the stream increases the efficiency of enzymatic hydrolysis by at least 7%.

2. 10. The method of claim 1, wherein the lignocellulosic feedstock is selected from softwood, forest residues, or a combination thereof.

3. Impregnation is done by mixing the processed raw material with SO ２ 10. The method of claim 1, comprising treating with

4. 10. The method of claim 1, wherein further processing of the impregnated slurry comprises heating at a temperature of 180-210°C and a pressure of 1.5-2 MPa for 5-30 minutes to obtain a treated slurry.

5. 10. The method of claim 1, wherein the concentration of the treated slurry is adjusted to about 15-25% w / w total solids by dilution with water or recycled water.

6. 10. The method of claim 1, wherein the pH of the treated slurry is adjusted to a range of 5.0 to 5.5 and further maintained at a temperature in the range of 52 to 55°C.

7. The method of claim 1 , wherein the additive is selected from polyhydroxy alcohols, glycols, nonionic surfactants, inorganic salts, and combinations thereof.

8. 8. The method of claim 7, wherein the additive is added at a rate ranging from 0.25 to 15% w / w of total solids at 50 to 55°C for 5 to 60 minutes.

9. 2. The method of claim 1, wherein the enzymatic hydrolysis is carried out with a cellulolytic enzyme mixture at a dosage ranging from 1 to 6%, at a pH ranging from 4.8 to 5.2, and at a temperature ranging from 50 to 55°C for 72 hours.

10. 10. The method of claim 9, wherein the enzymatically hydrolyzed stream comprises 4-8% glucose, 0.5-1.5% xylose, 0.2-0.5% galactose, and 2.0-3% mannose.

11. 10. The method of claim 1, wherein the co-fermenting of the enzymatically hydrolyzed stream to obtain a fermentation product is carried out using active dry yeast.

12. 12. The method of claim 11, wherein the fermentation product comprises ethanol.

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