Abstract:
A surfactant-improved simultaneous saccharification and co-fermentation method for lignocelluloses in which a pretreated lignocellulose substrate is directly subjected to surfactant-improved simultaneous saccharification and co-fermentation without any detoxification by adding a surfactant, and the surfactant may be selectively added before or after pre-enzymatic hydrolysis, having economic, effective and feasible application prospects in reducing the loss of glucose, simplifying the production process, reducing equipment investment, reducing water consumption, improving ethanol production and reducing the total cost of the ethanol production process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0001]    The present invention relates to the field of the production of fuel ethanol by the fermentation process of biomass feedstock degradation, and more particularly to a surfactant-improved simultaneous saccharification and co-fermentation method for lignocellulose. 
       2. Description of Related Arts 
       [0002]    With the increasing depletion of fossil fuels and the increasing pollution of the environment, the development and utilization of renewable clean energy fuels has received widespread attention. Traditional ethanol fermentation of sugar or starch as raw material, both of which are the main source of food, food as raw material to produce fuel ethanol has posed a threat to world food security, looking for other raw materials to replace food is imperative. Lignocellulose is the most abundant and inexpensive renewable resource in nature. Its main component cellulose hemicellulose is a potential raw material for the production of fuel ethanol. The production of fuel ethanol from lignocellulose has become a hot topic in the world. The production of fuel ethanol from lignocellulose is subject to three steps: pretreatment, enzymolysis and fermentation. However, toxic substances such as weak acid, furfural and 5-hydroxymethylfurfural (HMF) and phenolic compounds are produced during the biomass pretreatment: these compounds have a strong inhibitory effect on the fermentation of  Saccharomyces cerevisiae,  which affects the normal growth of yeast and the subsequent fermentation process. 
         [0003]    Therefore, it is particularly important to detoxify the pretreated lignocellulosic hydrolyzate. The detoxification methods reported in the literature mainly include water detoxification, physical detoxification (vacuum concentration gas extraction method, membrane separation method), chemical detoxification (lime neutralization, activated carbon adsorption, ion exchange, solvent extraction), biological detoxification, for example, Bioprocess Biosyst Eng (2013) 36: 659-666 discusses the effects of fermentation inhibitors such as furfural, HMF and levulinic acid on the growth rate of yeast cells by activated carbon adsorption. Patent No. CA102226204B discloses a lignocellulosic ethanol fermentation broth by adding a soluble electrolyte salt to the sugar solution to be treated and heating to obtain a constant temperature raw material liquid by membrane distillation to remove the saccharide from the subsequent fermentation to inhibit the role of substances. However, washing, physical, chemical detoxification, etc., consume a lot of water resources, equipment investment costs are high and the process is complex, and the detoxification effect is poor, sugar loss is serious; Yanling Yu reported a biological detoxification method (Bioresource Technology, 2011, (8): 5123-5128). The germination of corn stalk steam explosion was carried out by using Aspergillus nidulans (FLZ10), and then the fermentation was carried out by using  Saccharomyces cerevisiae.  The ethanol concentration reached 34 g/L. The method requires the addition of Aspergillus nidulans for equipment investment, culture medium and energy consumption. Therefore, the improvement of a simple, low cost, good detoxification process is the only way which must be passed for the wood fiber-ethanol industry. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is to provide a surfactant-improved simultaneous saccharification and co-fermentation method for lignocellulose in which the lignocellulose is used as a raw material, which is directed to the inhibitory effect of the toxic substances produced in the conventional biomass pretreatment process on the subsequent fermentation process. 
         [0005]    In order to achieve the object of the present invention, a surfactant-improved simultaneous saccharification and co-fermentation method (SSCF) for lignocellulose is provided by the present invention to directly treat the pretreated cellulose substrate without any detoxification treatment by continuously enzymatic hydrolysis; the surfactant may be optionally added before or after pre-enzymolysis. 
         [0006]    The specific steps of adding the surfactant to the pre-enzymatic solution are as follows: using the pretreated lignocellulose s a substrate, and adding firstly the cellulase, the water-soluble surfactant and the pH buffer under the high temperature condition for a period of time, and then lowering the temperature and adding  Saccharomyces cerevisiae  for simultaneous saccharification and ethanol fermentation production. 
         [0007]    When the surfactant is selectively added after pre-enzymatic hydrolysis, the specific steps are as follows: using the pre-treated lignocellulose as a substrate, and adding firstly the cellulase, a pH buffer under high temperature conditions for a period of time, and then lowering the temperature and adding the surfactant and  Saccharomyces cerevisiae  for simultaneous saccharification and ethanol fermentation. 
         [0008]    In the fermentation system, the solid-liquid ratio of the pretreated lignocellulose and the buffer is 0.1-0.3 g/mL; the concentration of the water-soluble surfactant is 0-0.4 g/mL; the loading of the cellulase added is 10-30 FPU/g dry lignocellulose, and the cell density of the  Saccharomyces cerevisiae  is 0.5*10 8 -1.8*10 8  cells/mL; the pre-enzymatic hydrolysis temperature is 50° C., the pre-enzymolysis time is 2-24 hours; and ethanol fermentation production temperature is 30-39° C.; simultaneous saccharification and ethanol fermentation time is 16-96 hours, 150-300 rpm. 
         [0009]    The surfactant includes at least one of polyethylene glycol (PEG), polyethylene glycol monomethyl ether (MPEG), polyethylene glycol dimethyl ether (NHD), polydimethylsiloxane (PMDS), or combinations thereof in any proportion. 
         [0010]    The water-soluble surfactant is preferably polyethylene glycol (PEG) having a molecular weight of from 200 to 8000, and more preferably from 200 to 2,000. 
         [0011]    The pH buffer solution of the table is: acetic acid-sodium acetate, citric acid-sodium citrate, phosphate-sodium phosphate buffer or sulfuric acid solution, the pH buffer solution has a pH value of 4.0-5.5. 
         [0012]    The pH value of the pH buffer solution is preferably 4.8. 
         [0013]    The concentration of the water-soluble surfactant is preferably 0.125-0.18 g/mL. 
         [0014]    The solid-liquid ratio of the pretreated lignocellulose and the buffer in the fermentation system is preferably 0.125 g/mL. 
         [0015]    The loading of the cellulase added in the fermentation system is preferably 20 FPU/g dry lignocellulose. 
         [0016]    The cell density of  Saccharomyces cerevisiae  in the fermentation system is preferably 0.6*10 8 -0.96*10 8  cells/mL. 
         [0017]    The pre-enzymatic hydrolysis time is preferably 8-12 hours; the temperature of the simultaneous saccharification and ethanol fermentation is preferably 33° C., and the simultaneous saccharification and ethanol fermentation time is preferably 72 hours. 
         [0018]    The specific SSCF process can be seen in  FIG. 1 ,  FIG. 2  and  FIG. 3 . 
         [0019]    The prior art utilizes pretreated lignocellulose as raw material, firstly add cellulase, a pH buffer under high temperature conditions for pre-enzymatic hydrolysis for a period of time, and then lower the temperature and add  Saccharomyces cerevisiae  for simultaneous saccharification and ethanol fermentation production, shown in  FIG. 1 . The process of the surfactant-improved lignocellulose simultaneous saccharification and co-fermentation method (SSCF) of the present invention is shown in  FIG. 2  and  FIG. 3 . 
         [0020]    Compared with the prior art, the present invention has the following advantages: the pretreated cellulose substrate can be directly fermented by continuous enzymatic saccharification and co-fermentation without detoxification via the addition of the surfactant, and it has economic, effective and feasible application prospects in reducing the loss of glucose, simplifying the production process, reducing equipment investment, reducing water consumption and improving ethanol production and so on. For the first time, the present invention ferments fast-growing poplar without detoxification by adding a surfactant and the simultaneous saccharification and co-fermentation method to produce ethanol, and the concentration and yield of ethanol has been improved and the total cost of the ethanol production process from lignocellulosic to ethanol is effectively reduced. 
         [0021]    For example, in the steam explosion process, the concentration of the pretreated fast-growing poplar is 15%, the simultaneous saccharification and co-fermentation time is 96 hours, when without the addition of the surfactant, the concentration of ethanol is 22% and 7.0 g/L, and when adding 1.5 g/mL surfactant, the yield and concentration of ethanol is 75% and 24.0 g/L, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  illustrates an operation of SSCF in pure water. 
           [0023]      FIG. 2  illustrates an operation 1 of a surfactant-improved SSCF. 
           [0024]      FIG. 3  illustrates an operation 2 of a surfactant-improved SSCF. 
           [0025]      FIG. 4  illustrates effects of different concentrations of PEG-1000 on enzymatic hydrolysis efficiency of non-detoxification steam exploded fast-growing poplar SSCF process. 
           [0026]      FIG. 5  illustrates effects of different concentrations of PEG-1000 on the ethanol yield of non-detoxification steam exploded fast-growing poplar SSCF process. 
           [0027]      FIG. 6  illustrates effects of different concentrations of PEG-1000 on the ethanol concentration of non-detoxification steam exploded fast-growing poplar SSCF process. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    The present invention will be described in further detail with reference to specific embodiments, but the scope of the invention is not to be limited by the scope of the present invention, and the following description of the invention and the description are merely illustrative of the principles of the present invention without departing from the spirit and scope of the present invention It will be understood that various changes and modifications may be made therein without departing from the scope of the present invention as claimed. It is intended that the scope of the present invention be defined by the appended claims and their equivalents. 
         [0029]    In addition, it is worth mentioning that the content of each component in the fermentation in each of the following examples is determined by a high performance liquid chromatograph (Agilent 1260), and the conversion rate and ethanol yield are calculated based on the amount of the dropped lignocellulosic substrate, and the ethanol concentration is calculated according to the mass of ethanol in the fermentation broth, the volume of activated water and the pH value thereof 
         [0030]    The conditions of chromatographic are as follows: ion exchange column, column temperature 65° C., parallax refractive index detector, detector temperature 50° C.; mobile phase: 5 Mm H 2 SO 4 , flow rate 0.6 mL/min, injection volume 25 uL. 
         [0031]    The pretreatment method described in the examples of the present invention is the steam explosion method. 
       EXAMPLE 1 
       [0032]    The pretreated fast-growing poplar powder of 1.5 g is used as a substrate, and firstly adding 10.5 mL buffer solution, 0.2 mL cellulase, wherein the buffer solution has a pH value of 4.86, incubating for 4 hours at a temperature of 50° C., and then lowering the temperature to 33° C., then adding  Saccharomyces cerevisiae,  wherein the cell density is maintained 0.8*10 8  /mL, SSCF fermentation for 72 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. 
       EXAMPLE 2 
       [0033]    The pretreated fast-growing poplar powder of 1.5 g is used as a substrate, and firstly adding 10.5 mL buffer solution, 0.2 mL cellulase and 2.0 g PEG-1000, wherein the buffer solution has a pH value of 4.86, incubating for 4 hours at a temperature of 50° C., and then lowering the temperature to 33° C., then adding  Saccharomyces cerevisiae,  wherein the cell density is maintained 0.8*10 8  /mL, SSCF fermentation for 72 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that the hydrolysis rate has almost no change after adding PEG-1000, while the ethanol yield and concentration is increased by nearly 1 times. 
       EXAMPLE 3 
       [0034]    The experimental procedure is the same as in Example 1 except that the yeast cell density is 0.96*10 8 /mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that the enzymatic efficiency, ethanol concentration and yield have almost no change after increasing the concentration of yeast cells in pure water system. 
       EXAMPLE 4 
       [0035]    The experimental procedure is the same as in Example 2 except that the yeast cell density is 0.96*10 8 /mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that in PEG-1000 system, when the concentration of yeast cells is increased, the enzymatic efficiency, ethanol concentration and yield have almost no change. 
       EXAMPLE 5 
       [0036]    The experimental procedure is the same as in Example 1 except that the buffer solution is increased to 12.0 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that in pure water system, when the concentration of substrate is reduced, the enzymatic efficiency, ethanol concentration and yield have almost no change. 
       EXAMPLE 6 
       [0037]    The experimental procedure is the same as in Example 2 except that the buffer solution is increased to 12.0 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that in PEG-1000 system, when the concentration of substrate is reduced, the enzymatic efficiency, ethanol concentration and yield are significantly improved. 
       EXAMPLE 7 
       [0038]    The experimental procedure is the same as in Example 1 except that the buffer solution is reduced to 10.0 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that in pure water system, when the concentration of substrate is increased, the enzymatic efficiency, ethanol concentration and yield have almost no change. 
       EXAMPLE 8 
       [0039]    The experimental procedure is the same as in Example 2 except that the buffer solution is reduced to 12.0 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 1. It can be seen from the data in the table that in PEG-1000 system, when the concentration of substrate is decreased, the enzymatic efficiency was decreased, ethanol concentration and yield are significantly increased. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Simultaneous saccharification and co-fermentation 
               
               
                 of pretreated fast-growing poplar 
               
             
          
           
               
                   
                 
                   Saccharomyces 
                 
                   
                   
                 Enzymatic 
                 Eth- 
                 Eth- 
               
               
                 Exam- 
                 
                   cerevisiae 
                 
                 PEG- 
                 Buffer/ 
                 hydrolysis 
                 anol 
                 anol/ 
               
               
                 ple 
                 cells/mL 
                 1000 
                 mL 
                 rate/% 
                 yield/% 
                 g/L 
               
               
                   
               
             
          
           
               
                 1 
                 0.8 × 10 8   
                 0.0000 
                 10.5 
                 62.2 
                 20.3 
                 7.57 
               
               
                 2 
                 0.8 × 10 8   
                 2.0901 
                 10.5 
                 62.7 
                 46.5 
                 17.30 
               
               
                 3 
                 0.96*10 8   
                 0.0000 
                 10.5 
                 62.8 
                 24.3 
                 9.05 
               
               
                 4 
                 0.96*10 8   
                 2.0072 
                 10.5 
                 58.1 
                 46.9 
                 17.46 
               
               
                 5 
                  0.8*10 8   
                 0.0000 
                 12.0 
                 67.1 
                 23.0 
                 7.52 
               
               
                 6 
                  0.8*10 8   
                 2.0209 
                 12.0 
                 65.5 
                 64.3 
                 20.94 
               
               
                 7 
                 0.96*10 8   
                 0.0000 
                 10.0 
                 64.5 
                 21.9 
                 8.55 
               
               
                 8 
                 0.96*10 8   
                 2.0342 
                 10.0 
                 58.3 
                 36.9 
                 14.44 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 9 
       [0040]    The experimental procedure is the same as in Example 5 except that the cellulase is 0.3 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that in pure water system, when the concentration of cellulase is improved, the enzymatic efficiency is increased a little, and ethanol concentration and yield have almost no change. 
       EXAMPLE 10 
       [0041]    The experimental procedure is the same as in Example 6 except that the cellulase is 0.3 mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that in PEG-1000 system, when the concentration of cellulase is improved, the enzymatic efficiency, ethanol concentration and yield are improved. 
       EXAMPLE 11 
       [0042]    The experimental procedure is the same as in Example 9 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis at 50° C. for 8 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that in pure water system, when the co-fermentation time is prolonged in pure water system, the enzymatic efficiency is increased, and ethanol concentration and yield have almost no change. 
       EXAMPLE 12 
       [0043]    The experimental procedure is the same as in Example 10 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis at 50° C. for 8 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that in pure water system, when the co-fermentation time is prolonged in the PEG-1000 system, the enzymatic efficiency, ethanol concentration and yield are improved. 
       EXAMPLE 13 
       [0044]    The experimental procedure is the same as in Example 12 except that PEG-1000 is added after the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that the order of addition of the surfactant has no significant effect on the fermentation efficiency. 
       EXAMPLE 14 
       [0045]    The experimental procedure is the same as in Example 10 except that PEG-1000 is 3.0 g. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 2. It can be seen from the data in the table that the excess of PEG-1000 can lead to the decrease of SSCF process efficiency, the enzymolysis efficiency, ethanol concentration and yield are reduced. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Simultaneous saccharification and co-fermentation 
               
               
                 of pretreated fast-growing poplar 
               
             
          
           
               
                   
                   
                   
                 Enzymolysis 
                 Ethanol 
                   
               
               
                 Example 
                 PEG-1000 
                 Time/h 
                 efficiency/% 
                 yield/% 
                 Ethanol/g/L 
               
               
                   
               
             
          
           
               
                 9 
                 0.0000 
                 4 + 72 
                 71.13 
                 23.28 
                 7.57 
               
               
                 10 
                 2.0039 
                 4 + 72 
                 72.12 
                 71.20 
                 23.17 
               
               
                 11 
                 0.0000 
                 8 + 72 
                 75.53 
                 22.52 
                 7.32 
               
               
                 12 
                 2.0085 
                 8 + 72 
                 76.51 
                 75.63 
                 24.61 
               
               
                 13 
                 2.0303 
                 8 + 72 
                 74.41 
                 73.44 
                 23.89 
               
               
                 14 
                 3.0300 
                 4 + 72 
                 62.16 
                 60.89 
                 19.81 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 15 
       [0046]    The experimental procedure is the same as in Example 11 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis for 24 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 3. It can be seen from the data in the table that in pure water system, the prolonged reaction time of SSCF process does not improve the ethanol concentration and yield. 
       EXAMPLE 16 
       [0047]    The experimental procedure is the same as in Example 12 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis for 24 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 3. It can be seen from the data in the table that in PEG-1000 system, the prolonged reaction time of SSCF process does not improve the ethanol concentration and yield. 
       EXAMPLE 17 
       [0048]    The experimental procedure is the same as in Example 15 except that the buffer solution is reduced to 10mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 3. It can be seen from the data in the table that in pure water system, when the concentration of substrate is increased in SSCF process, and the ethanol concentration is not improved. 
       EXAMPLE 18 
       [0049]    The experimental procedure is the same as in Example 12 except that the buffer solution is reduced to 10mL. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 3. It can be seen from the data in the table that in PEG-1000 system, when the concentration of substrate in SSCF process is increased, the ethanol yield and concentration are significantly reduced, but it is still higher than the pure water system. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Simultaneous saccharification and co-fermentation 
               
               
                 of pretreated fast-growing poplar 
               
             
          
           
               
                   
                   
                   
                 Enzymatic 
                   
                   
               
               
                   
                   
                   
                 hydrolysis 
                 Ethanol 
               
               
                 Example 
                 PEG-1000 
                 Buffer/mL 
                 rate/% 
                 yield/% 
                 Ethanol/g/L 
               
               
                   
               
             
          
           
               
                 15 
                 0.0000 
                 12 
                 82.88 
                 21.55 
                 7.01 
               
               
                 16 
                 2.0059 
                 12 
                 76.62 
                 75.74 
                 24.66 
               
               
                 17 
                 0.0000 
                 10 
                 77.41 
                 19.59 
                 7.65 
               
               
                 18 
                 1.9966 
                 10 
                 76.12 
                 28.42 
                 11.10 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 19 
       [0050]    The experimental procedure is the same as in Example 16 except that the fermentation temperature is 36oC. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 4. It can be seen from the data in the table that in PEG-1000 system, during the SSCF process, the proper increase of temperature can effectively improve the ethanol yield and concentration. 
       EXAMPLE 20 
       [0051]    The experimental procedure is the same as in Example 16 except that the fermentation temperature is 39oC. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in Table 4. It can be seen from the data in the table that in PEG-1000 system, during the SSCF process, the proper increase of temperature can effectively improve the ethanol yield and concentration. 
       EXAMPLE 21 
       [0052]    The experimental procedure is the same as in Example 16 except that the added surfactant is 2.0 g PEG-200. The enzymatic hydrolysis rate and ethanol concentration data are shown in Table 4. It can be seen from the data in the table that PEG-200 can effectively improve the ethanol yield and concentration. 
       EXAMPLE 22 
       [0053]    The experimental procedure is the same as in Example 16 except that the added surfactant is 2.0 g PEG-400. The enzymatic hydrolysis rate and ethanol concentration data are shown in Table 4. It can be seen from the data in the table that PEG-400 can effectively improve the ethanol yield and concentration. 
       EXAMPLE 23 
       [0054]    The experimental procedure is the same as in Example 16 except that the added surfactant is 2.0 g PEG-4000. The enzymatic hydrolysis rate and ethanol concentration data are shown in Table 4. It can be seen from the data in the table that PEG-4000 can effectively improve the ethanol yield and concentration. 
       EXAMPLE 24 
       [0055]    The experimental procedure is the same as in Example 16 except that the added surfactant is 2.0 g polyethylene glycol monomethyl ether (MPEG). The glucose conversion rate and ethanol concentration data are shown in Table 4. It can be seen from the data in the table that MPEG can effectively improve the ethanol yield and concentration. 
       EXAMPLE 25 
       [0056]    The experimental procedure is the same as in Example 16 except that the added surfactant is 2.0 g polyethylene glycol dimethyl ether (NHD). The glucose conversion rate and ethanol concentration data are shown in Table 4. It can be seen from the data in the table that NHD can effectively improve the ethanol yield and concentration. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Simultaneous saccharification and co-fermentation 
               
               
                 of pretreated fast-growing poplar 
               
             
          
           
               
                   
                   
                   
                 Enzymatic 
                   
                   
               
               
                   
                   
                 Temperature/ 
                 hydrolysis rate/ 
                 Ethanol 
                 Ethanol/ 
               
               
                 Example 
                 Surfactant 
                 ° C. 
                 % 
                 yield/% 
                 g/L 
               
               
                   
               
               
                 19 
                 PEG-1000 
                 55 + 36 
                 97.5 
                 96.8 
                 31.5 
               
               
                 20 
                 PEG-1000 
                 55 + 39 
                 89.1 
                 89.0 
                 29.0 
               
               
                 21 
                 PEG-200 
                 55 + 33 
                 77.4 
                 60.8 
                 19.8 
               
               
                 22 
                 PEG-400 
                 55 + 33 
                 76.1 
                 66.8 
                 22.8 
               
               
                 23 
                 PEG-4000 
                 55 + 33 
                 76.6 
                 75.7 
                 24.6 
               
               
                 24 
                 MPEG 
                 55 + 33 
                 77.2 
                 28.4 
                 11.1 
               
               
                 25 
                 NHD 
                 55 + 33 
                 74.5 
                 26.5 
                 10.0 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 26 
       [0057]    The pretreated fast-growing poplar powder of 1.5 g is used as a substrate, and firstly adding 12.0 mL buffer solution, 0.3 mL cellulase, 0-2.0 g surfactant, wherein the buffer solution has a pH value of 4.86, incubating for 24 hours at a temperature of 50° C., and then lowering the temperature to 33° C., then adding  Saccharomyces cerevisiae,  wherein the cell density is maintained 0.8*10 8  /mL, SSCF fermentation for 72 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in  FIGS. 4, 5 and 6 . It can be seen from the data in the Figs that PEG-1000 has little effect on the enzymolysis rate, while the ethanol yield and concentration increase with the increase of PEG-1000 concentration. 
       EXAMPLE 27 
       [0058]    The pretreated fast-growing poplar powder of 1.5 g is used as a substrate, and firstly adding 12.0 mL buffer solution, 0.3 mL cellulase, wherein the buffer solution has a pH value of 4.86, incubating for 4 hours at a temperature of 50° C., and then lowering the temperature to 33° C., then adding 1.5002 g surfactant of PEG-1000, wherein the cell density is maintained 0.8*108 /mL, SSCF fermentation for 72 hours. The enzymatic hydrolysis rate, ethanol yield and concentration data of the pretreated fast-growing poplar are shown in table 5. It can be seen from the data in the table that the addition order of PEG-1000 has no significant effect on the enzymolysis rate, the ethanol yield and concentration, as compared with Example 10 and Example 12. 
       EXAMPLE 28 
       [0059]    The experimental procedure is the same as in Example 27 except that the added surfactant is 2.0039 g PEG-1000. The enzymatic hydrolysis rate and ethanol concentration data are shown in Table 5. 
       EXAMPLE 29 
       [0060]    The experimental procedure is the same as in Example 27 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis for 8 hours, the enzymatic hydrolysis rate, ethanol yield and concentration data are shown in Table 5. 
       EXAMPLE 30 
       [0061]    The experimental procedure is the same as in Example 30 except that the pretreated fast-growing poplar is subjected to pre-enzymatic hydrolysis for 8 hours, and the added surfactant is 2.0103 g PEG-1000. The enzymatic hydrolysis rate, ethanol yield and concentration data are shown in Table 5. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Simultaneous saccharification and co-fermentation 
               
               
                 of pretreated fast-growing poplar 
               
             
          
           
               
                   
                   
                   
                 Enzymatic 
                   
                   
               
               
                   
                   
                   
                 hydrolysis 
                 Ethanol yield/ 
                 Ethanol/ 
               
               
                 Example 
                 PEG-1000 
                 Time/h 
                 rate/% 
                 % 
                 g/L 
               
               
                   
               
               
                 27 
                 1.5002 
                 4 + 72 
                 71.63 
                 71.42 
                 22.89 
               
               
                 28 
                 2.0039 
                 4 + 72 
                 71.82 
                 70.90 
                 22.17 
               
               
                 29 
                 1.5003 
                 8 + 72 
                 75.51 
                 74.63 
                 23.61 
               
               
                 30 
                 2.0103 
                 8 + 72 
                 74.93 
                 73.84 
                 24.01