Abstract:
A system for fermentation of biomass is disclosed. The system comprises a method for producing a fermentation product in a fermentation system from biomass that has been pre-treated and separated into a first component and a second component. The method comprises the steps of supplying the first component to the fermentation system; providing an ethanologen to the fermentation system; maintaining the first component and ethanologen in the fermentation system; and recovering the fermentation product from the fermentation system. A fermentation system configured to produce a fermentation product from biomass that has been pre-treated and separated into a first component and a second component is disclosed. The system comprises a first vessel configured to receive the first component and an ethanologen and a second vessel configured to propagate the ethanologen for supply to the first vessel. A biorefinery for producing a fermentation product from biomass is also disclosed. The biorefinery comprises a preparation system to prepare the biomass into prepared biomass; a pre-treatment system to pre-treat the prepared biomass with a dilute acid for separation into a first component from which pentose can accessed for fermentation and a second component from which hexose can be made available for fermentation; a first treatment system to treat the first component into a treated first component by removing removed components from the first component; a first fermentation system to produce a first fermentation product from the pentose; a distillation system to recover ethanol from the first fermentation product; and a treatment system to process removed components. The biomass comprises lignocellulosic material; the lignocellulosic material comprises at least one of corn cobs, corn plant husks, corn plant leaves and corn plant stalks. The first component comprises pentose; the pentose comprises xylose. The ethanologen is capable of fermenting xylose into ethanol.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and incorporates by reference each of the following applications: (a) U.S. Provisional Application Ser. No. 61/157,140, titled Process for Fermenting Pentose in Biomass, filed on Mar. 3, 2009; (b) U.S. Provisional Application Ser. No. 61/157,142, titled Continuous Fermentation of a Liquid Hydrolysate Containing Pentose, filed on Mar. 3, 2009; and (c) U.S. Provisional Application Ser. No. 61/157,137, titled Concentration of Pentose Liquor, filed on Mar. 3, 2009. 
         [0002]    The present application relates to and incorporates by reference the following applications: (a) U.S. Application Serial No. (Atty. Docket No. P184 1250.1), titled System for Pre-Treatment of Biomass for the Production of Ethanol, filed on Mar. 3, 2010; (b) U.S. Application Serial No. (Atty. Docket No. P184 1260.1), titled System for Treatment of Biomass to Facilitate the Production of Ethanol, filed on Mar. 3, 2010; and (c) U.S. Application Serial No. (Atty. Docket No. P184 1270.1), titled System for Management of Yeast to Facilitate the Production of Ethanol, filed on Mar. 3, 2010. 
     
    
     FIELD 
       [0003]    The present invention relates to a system for fermentation of biomass in the production of ethanol. The present invention also relates to a system for fermentation of biomass that has been pre-treated and separated into a first component and a second component. The present invention further relates to a system for fermentation of a first component of biomass using an ethanologen capable of fermenting xylose into ethanol. 
       BACKGROUND 
       [0004]    Ethanol can be produced from grain-based feedstocks (e.g. corn, sorghum/milo, barley, wheat, soybeans, etc.), from sugar (e.g. from sugar cane, sugar beets, etc.), and from biomass (e.g. from lignocellulosic feedstocks such as switchgrass, corn cobs and stover, wood or other plant material). 
         [0005]    Biomass comprises plant matter that can be suitable for direct use as a fuel/energy source or as a feedstock for processing into another bioproduct (e.g., a biofuel such as cellulosic ethanol) produced at a biorefinery (such as an ethanol plant). Biomass may comprise, for example, corn cobs and stover (e.g., stalks and leaves) made available during or after harvesting of the corn kernels, fiber from the corn kernel, switchgrass, farm or agricultural residue, wood chips or other wood waste, and other plant matter (grown for processing into bioproducts or for other purposes). In order to be used or processed, biomass will be harvested and collected from the field and transported to the location where it is to be used or processed. 
         [0006]    In a conventional ethanol plant producing ethanol from corn, ethanol is produced from starch. Corn kernels are cleaned and milled to prepare starch-containing material for processing. (Corn kernels can also be fractionated to separate the starch-containing material (e.g. endosperm) from other matter (such as fiber and germ).) The starch-containing material is slurried with water and liquefied to facilitate saccharification where the starch is converted into sugar (e.g. glucose) and fermentation where the sugar is converted by an ethanologen (e.g. yeast) into ethanol. The product of fermentation (i.e. fermentation product) is beer, which comprises a liquid component containing ethanol and water and soluble components, and a solids component containing unfermented particulate matter (among other things). The fermentation product is sent to a distillation system. In the distillation system, the fermentation product is distilled and dehydrated into ethanol. The residual matter (e.g. whole stillage) comprises water, soluble components, oil and unfermented solids (i.e. the solids component of the beer with substantially all ethanol removed that can be dried into dried distillers grains (DDG) and sold as an animal feed product). Other co-products, for example syrup (and oil contained in the syrup), can also be recovered from the stillage. Water removed from the fermentation product in distillation can be treated for re-use at the plant. 
         [0007]    In a biorefinery configured to produce ethanol from biomass, ethanol is produced from lignocellulosic material. Lignocellulosic biomass typically comprises cellulose, hemicellulose and lignin. Cellulose (a type of glucan) is a polysaccharide comprising hexose (C6) sugar monomers such as glucose linked in linear chains. Hemicellulose is .a branched chain polysaccharide that may comprise several different pentose (C5) sugar monomers (such as xylose and arabinose) and small amounts of hexose (C6) sugar monomers in branched chains. 
         [0008]    The biomass is prepared so that sugars in the lignocellulosic material (such as glucose from the cellulose and xylose from the hemicellulose) can be made accessible and fermented into a fermentation product from which ethanol can be recovered. After fermentation the fermentation product is sent to the distillation system, where the ethanol is recovered by distillation and dehydration. Other bioproducts such as lignin and organic acids may also be recovered as by-products or co-products during the processing of biomass into ethanol. Determination of how to more efficiently prepare and treat the biomass for production into ethanol will depend upon the source and type or composition of the biomass. Biomass of different types or from different sources is likely to vary in properties and composition (e.g. relative amounts of cellulose, hemicellulose, lignin and other components). For example the composition of wood chips will differ from the composition of corn cobs or switchgrass. 
         [0009]    It would be advantageous to provide for a system for treatment of biomass to facilitate the production of ethanol. It would also be advantageous to provide for a system to fermenting biomass for the production of ethanol. It would further be advantageous to provide for a system that provided one or more of features to facilitate improvement in the efficiency and yield of cellulosic ethanol from biomass. 
       SUMMARY 
       [0010]    The present invention relates to a method for producing a fermentation product in a fermentation system from biomass that has been pre-treated and separated into a first component and a second component. The method comprises the steps of supplying the first component to the fermentation system; providing an ethanologen to the fermentation system; maintaining the first component and ethanologen in the fermentation system at a temperature of between about 26 and about 37 degrees Celsius and at a pH of between about 4.5 and about 6.0 for a time of no less than 18 hours; and recovering the fermentation product from the fermentation system. The ethanologen is supplied to the fermentation system in a concentration of less than 150 grams of ethanologen on a dry basis per liter of first component. The biomass comprises lignocellulosic material; the lignocellulosic material comprises at least one of corn cobs, corn plant husks, corn plant leaves and corn plant stalks. The first component comprises pentose; the pentose comprises xylose. The ethanologen is capable of fermenting xylose into ethanol. 
         [0011]    The present invention also relates to a fermentation system configured to produce a fermentation product from biomass that has been pre-treated and separated into a first component and a second component. The system comprises a first vessel configured to receive the first component and an ethanologen and a second vessel configured to propagate the ethanologen for supply to the first vessel. The first vessel is configured to maintain the first component and ethanologen at a temperature of between about 31 and about 34 degrees Celsius and at a pH of between about 5.2 and about 5.8 for a time of no less than 18 hours. The biomass comprises lignocellulosic material; the lignocellulosic material comprises at least one of corn cobs, corn plant husks, corn plant leaves and corn plant stalks. The first component comprises pentose; the pentose comprises xylose. 
         [0012]    The present invention further relates to a biorefinery for producing a fermentation product from biomass. The biorefinery comprises a preparation system to prepare the biomass into prepared biomass; a pre-treatment system to pre-treat the prepared biomass with a dilute acid for separation into a first component from which pentose can accessed for fermentation and a second component from which hexose can be made available for fermentation; a first treatment system to treat the first component into a treated first component by removing removed components from the first component; a first fermentation system to produce a first fermentation product from the pentose by supplying an ethanologen and maintaining the first component and ethanologen at a temperature of between about 26 and about 37 degrees Celsius and at a pH of between about 4.5 and about 6.0 for a time of no less than  18  hours; a distillation system to recover ethanol from the first fermentation product; and a treatment system to process removed components. The biomass comprises lignocellulosic material; the lignocellulosic material comprises at least one of corn cobs, corn plant husks, corn plant leaves and corn plant stalks. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES AND TABLES 
         [0013]      FIG. 1A  is a perspective view of a biorefinery comprising a cellulosic ethanol production facility. 
           [0014]      FIG. 1B  is a perspective view of a biorefinery comprising a cellulosic ethanol production facility and a corn-based ethanol production facility. 
           [0015]      FIG. 2  is a schematic diagram of a system for receipt and preparation of biomass for a cellulosic ethanol production facility. 
           [0016]      FIG. 3  is a schematic block diagram of a system for the production of ethanol from biomass. 
           [0017]      FIGS. 4A ,  4 B and  4 C are schematic block diagrams of systems for treatment and processing of components from the production of ethanol from biomass. 
           [0018]      FIGS. 5A and 5B  are schematic diagrams of the process flow for systems for the production of ethanol from biomass. 
           [0019]      FIG. 6A  is a schematic block diagram of apparatus used for preparation, pre-treatment and separation of biomass. 
           [0020]      FIG. 6B  is a perspective view of apparatus used to pre-treat and separate the biomass. 
           [0021]      FIGS. 7A and 7B  are schematic block diagrams of a treatment system and fermentation system according to an exemplary embodiment. 
           [0022]      FIG. 8A  is a schematic block diagram of a system according to an exemplary embodiment, 
           [0023]      FIG. 8B  is a schematic block diagram of a fermentation system and treatment system according to an exemplary embodiment. 
           [0024]      FIGS. 9A and 9B  are perspective view of fermentation system according to exemplary embodiments. 
           [0025]      FIGS. 10A through 10D  are diagrams of operating conditions for the fermentation system according to an exemplary embodiment. 
           [0026]      FIG. 11  is a graph of results obtained through the use of the fermentation system according to an exemplary embodiment. 
           [0027]      FIGS. 12A and 12B  are a graph of results obtained through the use of the fermentation system according to an exemplary embodiment. 
           [0028]      FIGS. 13A and 13B  are a graph of results obtained through the use of the fermentation system according to an exemplary embodiment. 
           [0029]      FIG. 14  is a graph of results obtained through the use of the fermentation system according to an exemplary embodiment. 
       
    
    
       [0030]    TABLES 1A and 1B list the composition of biomass comprising lignocellulosic plant material from the corn plant according to exemplary and representative embodiments. 
         [0031]    TABLES 2A and 2B list the composition of the liquid component of pre-treated biomass according to exemplary and representative embodiments. 
         [0032]    TABLES 3A and 3B list the composition of the solids component of pre-treated biomass according to exemplary and representative embodiments. 
         [0033]    TABLES 4 through 7 provide data and results relating to the use of the fermentation system according to an exemplary embodiment. 
       DETAILED DESCRIPTION 
       [0034]    Referring to  FIG. 1A , a biorefinery configured to produce ethanol from biomass is shown. 
         [0035]    According to an exemplary embodiment, the biorefinery is configured to produce ethanol from biomass in the form of a lignocellulosic feedstock such as plant material from the corn plant (e.g. corn cobs and corn stover). Lignocellulosic feedstock such as lignocellulosic material from the corn plant comprises cellulose (from which C6 sugars such as glucose can be made available) and/or hemicellulose (from which C5 sugars such as xylose and arabinose can be made available). 
         [0036]    As shown in  FIG. 1A , the biorefinery comprises an area where biomass is delivered and prepared to be supplied to the cellulosic ethanol production facility. The cellulosic ethanol production facility comprises apparatus for preparation, pre-treatment and treatment of the biomass into treated biomass suitable for fermentation into fermentation product in a fermentation system. The facility comprises a distillation system in which the fermentation product is distilled and dehydrated into ethanol. As shown in  FIG. 1A , the biorefinery may also comprise a waste treatment system (shown as comprising an anaerobic digester and a generator). According to other alternative embodiments, the waste treatment system may comprise other equipment configured to treat, process and recover components from the cellulosic ethanol production process, such as a solid/waste fuel boiler, anaerobic digester, aerobic digester or other biochemical or chemical reactors. 
         [0037]    As shown in  FIG. 1B , according to an exemplary embodiment, a biorefinery may comprise a cellulosic ethanol production facility (which produces ethanol from lignocellulosic material and components of the corn plant) co-located with a corn-based ethanol production facility (which produces ethanol from starch contained in the endosperm component of the corn kernel). As indicated in  FIG. 1B , by co-locating the two ethanol production facilities, certain plant systems may be shared, for example, systems for dehydration, storage, denaturing and transportation of ethanol, energy/fuel-to-energy generation systems, plant management and control systems, and other systems. Corn fiber (a component of the corn kernel), which can be made available when the corn kernel is prepared for milling (e.g. by fractionation) in the corn-based ethanol production facility, may be supplied to the cellulosic ethanol production facility as a feedstock. Fuel or energy sources such as methane or lignin from the cellulosic ethanol production facility may be used to supply power to either or both co-located facilities. According to other alternative embodiments, a biorefinery (e.g. a cellulosic ethanol production facility) may be co-located with other types of plants and facilities, for example an electric power plant, a waste treatment facility, a lumber mill, a paper plant or a facility that processes agricultural products. 
         [0038]    Referring to  FIG. 2 , a system for preparation of biomass delivered to the biorefinery is shown. The biomass preparation system may comprise apparatus for receipt/unloading of the biomass, cleaning (i.e. removal of foreign matter), grinding (i.e. milling, reduction or densification), and transport and conveyance for processing at the plant. According to an exemplary embodiment, biomass in the form of corn cobs and stover may be delivered to the biorefinery and stored (e.g. in bales, piles or bins, etc.) and managed for use at the facility. According to a preferred embodiment, the biomass may comprise at least 20 to 30 percent corn cobs (by weight) with corn stover and other matter. According to other exemplary embodiments, the preparation system of the biorefinery may be configured to prepare any of a wide variety of types of biomass (i.e. plant material) for treatment and processing into ethanol and other bioproducts at the plant. 
         [0039]    Referring to  FIG. 3 , a schematic diagram of the cellulosic ethanol production facility is shown. According to a preferred embodiment, biomass comprising plant material from the corn plant is prepared and cleaned at a preparation system. After preparation, the biomass is mixed with water into a slurry and is pre-treated at a pre-treatment system. In the pre-treatment system, the biomass is broken down (e.g. by hydrolysis) to facilitate separation into a liquid component (e.g. a stream comprising the C5 sugars) and a solids component (e.g. a stream comprising cellulose from which the C6 sugars can be made available). The C5-sugar-containing liquid component (C5 stream) and C6-sugar-containing solids component (C6 stream) can be treated (as may be suitable) and fermented in a fermentation system. Fermentation product from the fermentation system is supplied to a distillation system where the ethanol is recovered. 
         [0040]    As shown in  FIGS. 3 and 4A , removed components from treatment of the C5 stream can be treated or processed to recover by-products, such as organic acids and furfural. As shown in  FIGS. 3 and 4B , removed components from treatment of the C6 stream, such as lignin or other components, can be treated or processed into bioproducts or into fuel (such as lignin for a solid fuel boiler or methane produced by treatment of residual/removed matter such as acids and lignin in an anaerobic digester). As shown in  FIGS. 4A ,  4 B and  4 C, components removed during treatment and production of ethanol from the biomass from either or both the C5 stream and the C6 stream (or at distillation) may be processed into bioproducts (e.g. by-products or co-products) or recovered for use or reuse. As shown in  FIG. 4C , removed components from the distillation system (such as stillage or removed solids) or from the treatment of the fermentation product before distillation (e.g. removed solids and particulate matter, which may comprise residual lignin, etc.) can be treated or processed into bioproducts or fuel (e.g. methane produced in an anaerobic digester). 
         [0041]    According to a preferred embodiment, the biomass comprises plant material from the corn plant, such as corn cobs, husks and leaves and stalks (e.g. at least upper half or three-quarters portion of the stalk); the composition of the plant material (i.e. cellulose, hemicellulose and lignin) will be approximately as indicated in TABLES 1A and 1B (i.e. after at least initial preparation of the biomass, including removal of any foreign matter). According to a preferred embodiment, the plant material comprises corn cobs, husks/leaves and stalks; for example, the plant material may comprise (by weight) up to 100 percent cobs, up to 100 percent husks/leaves, approximately 50 percent cobs and approximately 50 percent husks/leaves, approximately 30 percent cobs and approximately 50 percent husks/leaves and approximately 20 percent stalks, or any other combinations of cobs, husks/leaves and stalks from the corn planta See TABLE 1A. According to an alternative embodiment, the lignocellulosic plant material may comprise fiber from the corn kernel (e.g. in some combination with other plant material). TABLE 1B provides typical and expected ranges believed to be representative of the composition of biomass comprising lignocellulosic material from the corn plant. According to exemplary embodiments, the lignocellulosic plant material of the biomass (from the corn plant) will comprise (by weight) cellulose at about 30 to 55 percent, hemicellulose at about 20 to 50 percent, and lignin at about 10 to 25 percent; according to a particularly preferred embodiment, the lignocellulosic plant material of the biomass (i.e. cobs, husks/leaves and stalk portions from the corn plant) will comprise (by weight) cellulose at about 35 to 45 percent, hemicellulose at about 24 to 42 percent, and lignin at about 12 to 20 percent. According to a particularly preferred embodiment, pre-treatment of the biomass will yield a liquid component that comprises (by weight) xylose at no less than 1.0 percent and a solids component that comprises (by weight) cellulose (from which glucose can be made available) at no less than 45 percent. 
         [0042]    Referring to  FIGS. 5A and 5B , exemplary embodiments of systems for the production of ethanol from biomass are shown. As shown in  FIGS. 5A and 5B , biomass is pre-treated in a pre-treatment system and then separated into a liquid component and a solids component. 
         [0043]    According to a preferred embodiment, in the pre-treatment system an acid will be applied to the prepared biomass to facilitate the break down of the biomass for separation into the liquid component (C5 stream from which fermentable C5 sugars can be recovered) and the solids component (C6 stream from which fermentable C6 sugars can be accessed). According to a preferred embodiment, the acid can be applied to the biomass in a reaction vessel under determined operating conditions (i.e. acid concentration, pH, temperature, time, pressure, solids loading, flow rate, supply of process water or steam, etc.) and the biomass can be agitated/mixed in the reaction vessel to facilitate the break down of the biomass. According to exemplary embodiments, an acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, etc. (or a formulation/mixture of acids) can be applied to the biomass. According to a particularly preferred embodiment, sulfuric acid will be applied to the biomass in pre-treatment. 
         [0044]    The liquid component (C5 stream) comprises water, dissolved sugars (such as xylose, arabinose and glucose) to be made available for fermentation into ethanol, acids and other soluble components recovered from the hemicellulose. (TABLE 2B provides typical and expected ranges believed to be representative of the composition of biomass comprising lignocellulosic material from the corn plant.) According to an exemplary embodiment, the liquid component may comprise approximately 5 to 7 percent solids (i.e. suspended/residual solids such as partially-hydrolyzed hemicellulose, cellulose and lignin). According to a particularly preferred embodiment, the liquid component will comprise at least 2 to 4 percent xylose (by weight); according to other exemplary embodiments, the liquid component will comprise no less than 1 to 2 percent xylose (by weight). TABLES 2A and 2B list the composition of the liquid component of pre-treated biomass (from prepared biomass as indicated in TABLES 1A and 1B) according to exemplary and representative embodiments. 
         [0045]    The solids component (C6 stream) comprises water, acids and solids such as cellulose from which sugar, such as glucose, can be made available for fermentation into ethanol, and lignin. (TABLE 3B provides typical and expected ranges believed to be representative of the composition of biomass comprising lignocellulosic material from the corn plant.) According to an exemplary embodiment, the solids component may comprise approximately 10 to 40 percent solids (by weight) (after separation); according to a particularly preferred embodiment, the solids component will comprise approximately 20 to 30 percent solids (by weight). According to a preferred embodiment, the solids in the solids component comprise no less than 30 percent cellulose and the solids component may also comprise other dissolved sugars (e.g. glucose and xylose). TABLES 3A and 3B list the composition of the solids component of pre-treated biomass (from prepared biomass as indicated in TABLES 1A and 1B) according to exemplary and representative embodiments. 
         [0046]    During pre-treatment, the severity of operating conditions (such as pH, temperature and time) may cause formation of components that are inhibitory to fermentation. For example, under some conditions, the dehydration of C5 sugars (such as xylose or arabinose) may cause the formation of furfural and/or hydroxymethylfurfural (HMF). Acetic acid may also be formed, for example when acetate is released during the break down of cellulose in pre-treatment. Sulfuric acid, which may be added to prepared biomass to facilitate pre-treatment, if not removed or neutralized, may also be inhibitory to fermentation. According to an exemplary embodiment, by adjusting pre-treatment conditions (such as pH, temperature and time), the formation of inhibitors can be reduced or managed; according to other exemplary embodiments, components of the pre-treated biomass may be given further treatment to remove or reduce the level of inhibitors (or other undesirable matter). 
         [0047]    Referring to  FIGS. 5A and 5B , after pre-treatment and separation the C5 stream and the C6 stream are processed separately; as shown, the C5 stream and the C6 stream may be processed separately prior to co-fermentation (C5/C6 fermentation as shown in  FIG. 5A ) or processed separately including separate fermentation (separate C5 fermentation and C6 fermentation as shown in  FIG. 5B ). 
         [0048]    Treatment of the C5 stream (liquid component) of the biomass may be performed in an effort to remove components that are inhibitory to efficient fermentation (e.g. furfural, HMF, sulfuric acid and acetic acid) and residual lignin (or other matter) that may not be fermentable from the C5 sugar component so that the sugars (e.g. xylose, arabinose, as well as other sugars such as glucose) are available for fermentation. The C5 sugars in the C5 stream may also be concentrated to improve the efficiency of fermentation (e.g. to improve the titer of ethanol for distillation). 
         [0049]    Treatment of the C6 stream (solids component) of the biomass may be performed to make the C6 sugars available for fermentation. According to a preferred embodiment, hydrolysis (such as enzyme hydrolysis) may be performed to access the C6 sugars in the cellulose; treatment may also be performed in an effort to remove lignin and other non-fermentable components in the C6 stream (or to remove components such as residual acid or acids that may be inhibitory to efficient fermentation). 
         [0050]    According to an exemplary embodiment shown in  FIG. 5A , after pre-treatment and separation the C5 stream and the C6 stream can be treated separately and subsequently combined after treatment (e.g. as a slurry) for co-fermentation in the fermentation system to produce a C5/C6 fermentation product from the available sugars (e.g. xylose and glucose); the C5/C6 fermentation product can (after treatment, if any) be supplied to the distillation system for recovery of the ethanol (e.g. through distillation and dehydration). According to an exemplary embodiment shown in  FIG. 5B , the C5 stream and the C6 stream can each be separately processed through fermentation and distillation (after treatment, it any) to produce ethanol. According to any preferred embodiment, a suitable fermenting organism (ethanologen) will be used in the fermentation system; the selection of an ethanologen may be based on various considerations, such as the predominant types of sugars present in the slurry. Dehydration and/or denaturing of the ethanol produced from the C5 stream and the C6 stream may be performed either separately or in combination. 
         [0051]      FIG. 6A and 6B  show the apparatus used for preparation, pre-treatment and separation of lignocellulosic biomass according to an exemplary embodiment. As shown, biomass is prepared in a grinder (e.g. grinder or other suitable apparatus or mill). Pre-treatment of the prepared biomass is performed in a reaction vessel (or set of reaction vessels) supplied with prepared biomass and acid/water in a predetermined concentration (or pH) and other operating conditions. As shown in  FIG. 6B , the pre-treated biomass can be separated in a centrifuge into a liquid component (C5 stream comprising primarily liquids with some solids) and a solids component (C6 stream comprising liquids and solids such as lignin and cellulose from which glucose can be made available by further treatment). 
         [0052]    Referring to  FIGS. 7A and 7B , a treatment system and fermentation system for the liquid component (C5 stream or hydrolysate) of the pre-treated biomass is shown. As shown in  FIG. 7B , according to an exemplary embodiment, the treatment system can comprise filtration of the C5 stream to remove inhibitors (such as furfural and acetic acid) and concentration of the C5 stream to facilitate the efficient fermentation of sugars (e.g. xylose and glucose). As shown in  FIG. 8A , according to an exemplary embodiment, the fermentation system can comprise the fermentation of the C5 stream by the application of an ethanologen (i.e. an organism shown as yeast cells) and agents (such as nutrients) for the ethanologen to yield a fermentation product. 
         [0053]    According to an exemplary embodiment, the fermentation product is produced in the fermentation system by application of the ethanologen to convert the sugars in the C5 stream (hydrolysate of the pre-treated biomass) into ethanol. According to a preferred embodiment, the ethanologen for the fermentation system may comprise an organism (i.e. yeast) selected for efficient fermentation of the xylose and glucose that is present in the C5 stream. According to a particularly preferred embodiment, the ethanologen for the C5 stream may be a genetically modified organism as described in U.S. Pat. No. 7,622,284, assigned to Royal Nedalco B. V. According to an alternative embodiment, the ethanologen may comprise a formulation or combination of organisms (e.g. one type of yeast selected for fermentation of C5 sugars such as xylose and one type of yeast selected for fermentation of C6 sugars such as glucose). According to exemplary embodiments, the amount or loading (dose) of ethanologen (i.e. yeast cells) may be varied in the operation of the fermentation system. Agents supplied with the ethanologen may include antibiotics, supplemental or accessory enzymes, urea, salts (such as zinc or magnesium salts), or other component providing nutritional or other benefit to the organism. 
         [0054]    Referring to  FIGS. 9A and 9B , the fermentation system may operate in a batch, fed batch, continuous flow, or Other arrangement. According to an exemplary embodiment, the fermentation system will comprise at least one fermentation tank. According to the exemplary embodiment shown in  FIG. 9A , the fermentation system comprises a set of tanks into which the treated C5 stream (i.e. treated hydrolysate from pre-treated biomass, in a slurry) is supplied, along with the ethanologen and nutrients (as needed). As shown in  FIGS. 9A and 9B , ethanologen (shown as yeast) is supplied from a yeast propagation system comprising a tank (maintained under operating conditions suitable for growth of a suitable quantity of yeast/organism from seed or source). Fermentation is conducted under operating conditions selected to facilitate the efficient conversion of the sugars in the C5 stream/hydrolysate into ethanol. operating conditions for the fermentation system will comprise time, temperature, pH, solids loading and ethanologen loading. 
         [0055]    According to an exemplary embodiment using batch fermentation, as shown in  FIG. 9A , the fermentation system comprises multiple tanks and is configured so that fermentation can be conducted simultaneously in multiple fermentation tanks. The slurry (treated hydrolysate/C5 stream), ethanologen and nutrients will be supplied to each of the fermentation tanks according to a sequence. Fermentation will be performed for a designated period of time under the designated operating conditions for each particular tank; after fermentation has been completed in the particular tank, the tank will then be emptied of fermentation product and cleaned. According to a preferred embodiment, one tank will be available to receive and be filled with slurry as it is produced; fermentation will be taking place in at least one other tank; and another tank in which fermentation has been completed may be being emptied and readied to be filled and used for another fermentation. The operating conditions for fermentation (as well as samples of the slurry being fermented) may be monitored and controlled in each fermentation tank. 
         [0056]    According to an exemplary embodiment using continuous fermentation, as shown in  FIG. 9B , the fermentation system comprises multiple tanks in a cascade arrangement. The fermentation system is configured so that the slurry (treated hydrolysate/C5 stream) and ethanologen/nutrients are initially supplied to a first tank. As fermentation proceeds in the tank, partially-fermented slurry in the process of being fermented is flowed into the next tank in sequence; when emptied from the final tank, the slurry has been completely fermented into fermentation product. The operating conditions for fermentation (as well as samples of the slurry being fermented) may be monitored and controlled in each fermentation tank. 
         [0057]    The fermentation product (which may also be referred to as beer or fermentation broth, or as comprising beer or fermentation broth) will comprise ethanol and water, as well as unfermented matter (e.g. any unfermented sugars) and non-fermentable matter (e.g. residual lignin and other solids). The fermentation product will also comprise in the form of particulate matter the ethanologen (i.e. yeast cells) that was used to produce ethanol, as well as other components produced by the fermentation system, for example, such as glycerol (a product of fermentation) and acetic acid. 
         [0058]    As shown in  FIG. 8B , according to an exemplary embodiment, a treatment system for the fermentation product may also be provided. The treatment system can comprise separation of the fermentation product into a liquid component (i.e. a treated fermentation product, which will comprise substantially ethanol and water) and a solids component (which will comprise substantially solids matter such as the ethanologen/yeast cells). According to a preferred embodiment, as shown in  FIG. 8B , the separation of the fermentation product into the liquid component and solids component can be performed on a centrifuge; according to other exemplary embodiments, the separation may be performed in other apparatus (or other equipment configured to separate solids and liquids). As shown in  FIG. 8B , the solids component from treatment comprising the yeast cells can be supplied to and re-used in the fermentation system (i.e. recycled for use in a fermentation tank) along with additional or fresh yeast cells (if necessary). 
         [0059]    As shown in  FIGS. 2 ,  5 A and  5 B, the liquid component (or treated fermentation product) from the treatment system can be supplied to the distillation system, for distillation and dehydration to allow recovery of ethanol. 
         [0060]      FIGS. 10A through 10D  show operating conditions for subject parameters of the fermentation system according to an exemplary embodiment of the system (configured for the fermentation of the treated liquid component/C5 stream of biomass in the form of corn cobs and stover, following acid pre-treatment and separation); operating conditions are shown in the form of nested ranges comprising an acceptable operating range (the outer/wide range shown), a preferred operating range (the middle range shown), and a particularly preferred operating range (the inner/narrow range shown) for each subject condition or parameter. 
         [0061]      FIG. 10A  shows the temperature ranges for operation of a fermentation system according to exemplary embodiments. According to an exemplary embodiment, the operating temperature range is about to about 37 degrees Celsius. According to a preferred embodiment, the operating temperature is from about 30 to about 34 degrees Celsius. According to a particularly preferred embodiment, the operating temperature is from about 31 to about 34 degrees Celsius. 
         [0062]      FIG. 10B  shows the pH ranges for operation of a fermentation system according to exemplary embodiments. According to an exemplary embodiment, the pH range is about 3.7 to about 6.5. According to a preferred embodiment, the pH is from about 4.5 to about 6.0. According to a particularly preferred embodiment, the pH is from about 5.4 to about 5.6. 
         [0063]      FIG. 10C  shows the yeast loading (in grams of dry yeast per liter of hydrolysate) for operation of a fermentation system according to exemplary embodiments (for example, a genetically modified yeast derived from the organism disclosed in U.S. Pat. No. 7,622,284, incorporated by reference, assigned to Royal Nedalco, B. V.). According to an exemplary embodiment, the yeast loading is about 0.05 to about 35 grams per liter. According to a preferred embodiment, the yeast loading is from about 5 to about 20 grams per liter. According to a particularly preferred embodiment, the yeast loading is from about 10 to about 15 grams per liter. 
         [0064]      FIG. 10D  shows the time for operation of a batch fermentation system according to exemplary embodiments (excluding of time to fill and empty the fermentation tank). According to an exemplary embodiment, the fermentation time is about 12 to 144 hours. According to a preferred embodiment, the fermentation time is about 18 to 96 hours. According to a particularly preferred embodiment, the fermentation time is about 24 to 48 hours. 
         [0065]    According to other alternative embodiments, for example, using a different form or type of biomass or a different ethanologen, the operating conditions for the fermentation system may be varied as necessary to achieve efficient fermentation. 
         [0066]    A series of examples were conducted according to an exemplary embodiment of the fermentation system (as shown in  FIGS. 11 through 14 ) in an effort to evaluate efficacy for fermentation of sugars from the C5 stream (e.g. liquid component from separation of pre-treated biomass). The ethanologen used in the examples was a strain of Saccharomyces cerevisiae yeast altered to convert xylose and glucose to ethanol (a genetically modified yeast derived from an organism as described in U.S. Pat. No. 7,622,284 by Royal Nedalco B. V., for example strain No. RWB218 and strain No. RN1001). Data from the examples is shown in TABLES 4 through 7. The biomass comprised corn cobs and stover. 
       EXAMPLE 1 
       [0067]    The fermentation system was used in Example 1 to evaluate the effect of ethanologen loading on the efficacy of the ethanologen in the fermentation of xylose into ethanol, as indicated in  FIG. 11 . The ethanologen was yeast (strain No. RWB218.) A sample was prepared having an initial xylose concentration of about 4.7 percent (by weight). The sample was divided into subsamples, which were supplied with a yeast loading between about 0.05 and 30 grams per liter (of sample) in a fermentation system to produce a fermentation product. The fermentation was conducted at approximately 32 degrees Celsius and approximately pH 5.5 for approximately 48 hours. The subsamples were analyzed for xylose concentration and ethanol concentration. It was observed that at least about 5 grams per liter of yeast was needed for sufficient fermentation of xylose to ethanol under the operating conditions. The results are shown in  FIG. 11  and TABLE 4. 
       EXAMPLE 2A 
       [0068]    The fermentation system was used in Example 2A to evaluate the efficacy of the ethanologen in the fermentation of xylose in a hydrolysate from the liquid component (i.e. C5 stream) of pre-treated biomass at varying levels of initial loading (i.e. yeast concentration), as indicated in  FIGS. 12A and 12B . The ethanologen was yeast (strain No. RWB218.) A sample of the hydrolysate was prepared including about 4.7 percent xylose (by weight). The sample was divided into subsamples, which were supplied with a yeast loading between about 0.5 and 30 grams per liter (of sample) in a fermentation system to produce a fermentation product. The fermentation was conducted at approximately 32 degrees Celsius and approximately pH 5.5 for approximately 72 hours. The subsamples were analyzed for xylose concentration and ethanol concentration at 24 hours, 48 hours and about 72 hours (the end of fermentation). It was observed that at least about 5 grams per liter of yeast was needed for sufficient fermentation of xylose to ethanol and that efficient fermentation could be achieved at about 10 grams per liter under the operating conditions. The results are shown in  FIGS. 12A and 12B  and TABLES 5A and 5B. 
       EXAMPLE 2B 
       [0069]    The fermentation system was used in Example 2B to evaluate the efficacy of the ethanologen in the fermentation of xylose in a hydrolysate from the liquid component (i.e. C5 stream) of pre-treated biomass at varying levels of initial loading (i.e. yeast concentration), as indicated in  FIGS. 13A and 13B . The ethanologen was yeast (strain No. RN1001.) A sample of the hydrolysate was prepared comprising about 3.1 to 3.2 percent xylose (by weight) and less than 3800 PPM of acetic acid. The sample was divided into subsamples, which were supplied with a yeast loading between about 0.1 and 30 grams per liter (of sample) in a fermentation system to produce a fermentation product. The fermentation was conducted at approximately 32 degrees Celsius and approximately pH 5.5 for approximately 72 hours. The subsamples were analyzed for xylose concentration and ethanol concentration at 6 hours, 12 hours, 18 hours, 24 hours, 48 hours and about 72 hours (the end of fermentation). It was observed that at least about 1 gram per liter of yeast was needed for sufficient fermentation of xylose to ethanol under the operating conditions. The results are shown in  FIGS. 13A and 13B  and TABLE 6. 
       EXAMPLE 3 
       [0070]    The fermentation system was used in Example 3 to evaluate the effect of xylose concentration on the efficacy (and xylose tolerance) of the ethanologen in the fermentation of xylose into ethanol, as indicated in  FIG. 14 . The ethanologen was yeast (strain No. RWB218.) A sample was prepared using a sterile medium comprising 1 gram per liter (of sample) yeast extract and 1 gram per liter (of sample) soy peptone and an initial yeast loading (inoculation rate) of about 0.59 grams per liter (of sample). The sample was divided into subsamples and supplied to a fermentation system to produce a fermentation product; subsamples were fermented with initial xylose concentrations between about 2.3 percent and 17.6 percent (by weight). The fermentation was conducted at approximately 32 degrees Celsius and approximately pH 5.5 for approximately 72 hours. The subsamples were analyzed for xylose concentration and ethanol concentration at 72 hours (the end of fermentation). It was observed that the yeast was able to convert xylose to ethanol at a xylose concentration at and below approximately 11.3 percent (by weight), but was no longer efficient at a xylose concentration at or above approximately 13.6 percent (by weight) under the operating conditions. The results are shown in  FIG. 14  and TABLE 7. 
         [0071]    The embodiments as disclosed and described in the application (including the FIGURES and Examples) are intended to be illustrative and explanatory of the present inventions. Modifications and variations of the disclosed embodiments, for example, of the apparatus and processes employed (or to be employed) as well as of the compositions and treatments used (or to be used), are possible; all such modifications and variations are intended to be within the scope of the present inventions.