| Lignocellulosic ethanol production have been become one of lobal hot issue, However, it is necessary for the use of lignocellulosic ethanol production to make a breakthrough in the restriction of technologies converting lignocellulosic biomass into available sugar.Therefore the pretreatment process is used widely. Almost of all the present pretreatment methods, however, have disadvantages in high cost, serious pollution and low efficiency and so on. In order to reduce the cost of pretreatment, and to enhance enzymatic efficiency and ethanol production, in this study, we performed pretreatment experiments of bagasse and water hyacinth by using a combination of H2O2alkaline pretreatment method and an ionic liquid method.We analyzed the physicochemical properties and characteristics of the enzymatic hydrolysis and fermentation. The main findings are as follows:1.The lignocellulosic pretreatment and enzymatic hydrolysis of bagasse and water hyacinthSingle factor and orthogonal experimental methods were applied for optimization of NaOH/H2O2pretreatment conditions. We measured the samples of cellulose, hemicellulose and lignin content. The efficiency of pretreatment was evaluated by using the data of the removal rate, the cellulose hydrolysis rate, and the crystallinity values.The experimental results show that under the condition that the solid-liquid ratio is1:25, the optimum NaOH/H2O2pretreatment condition of bagasse is3%NaOH,1%H2O2,12h and42℃. Under this processing condition, hemicellulose and lignin removal rates of the samples were78.2%and93.6%, respectively. Cellulose hydrolysis rate was61.8%. Compared with the original untreated material, cellulose hydrolysis rate was increased by56.9%.In the meanwhile, the optimum of water hyacinth NaOH/H2O2pretreatment condition is1.5%H2O2,3%NaOH,24h,25℃. Under this processing conditions, hemicellulose and lignin removal rates in the samples were74.5%and42.1%,respectively, and cellulose hydrolysis rate was58.1%. Compared to the rate of hydrolysis of the raw materials, It was increased by about45%. The enzymatic hydrolysis of the sample was promoted significantly. In this study, we also conducted the experiments of ionic liquid (BMIMC1) pretreatment in terms of different times (30,60,90,120min) and different temperatures (80,100,120,140℃).The results showed that under the condition that the ratio of raw material and BMIMCl is1:20, the optimum BMIMCl pretreatment condition of bagasse is140℃,60min. Under this processing condition, cellulose hydrolysis rate was20.3%, compared with the original untreated material, cellulose hydrolysis rate was increased by16.4%. The optimum BMIMC1pretreatment conditions of water hyacinth is100℃,60min, under this processing conditions, cellulose hydrolysis rate was33.8%, compared with the untreated material, cellulose hydrolysis rate was increased by22.16%.2. High-temperature ethanol fermentation of pretreated bagasse and water hyacinthIn this study, thermotolerant yeast K. marxianus K213, Ogataea sp WXT3and K. marxianus S16were used as fermented strains, and Angel Yeast (S. cerevisiae) was used as a control, the thermotolerant yeast was screened by our laboratory. Each raw material was treated under the optimum condition for preparing the substrate. We used these subsrate to conduct the experiment of separately hydrolysis fermentation and simultaneous saccharification fermentation.Fermentation characteristics were comp-areed by measuring ethanol production under the different conditions.The results showed that the pretreated bagasse fermented by the K. marxianus K213, Ogataea sp. WXT3, K.marxianus S16and S.cerevisiae. In the SHF fermentation show that K. marxianus K213, Ogataea sp. WXT3, K.marxianus S16, and S.cerevisiae strains consumed20.58g/1,20.70g/l,20.31g/l, and20.24g/l of glucose hydrolyzate was used as substrate, respectively, and yields7.25g/l,6.74g/1,6.71g/l and8.08g/l of ethanol, respectively. Conversion rates of each strain were0.35g/g,0.32g/g,0.33g/g, and0.40g/g, respectively. These data were69.1%,63.8%,64.8%and78.3%of the theoretical conversion rate, respectively. In the SSF fermentation, the four strains the maximum ethanol yields were8.68g/1,8.80g/l,9.75g/1and4.40g/l, and significantly higher than the SHF fermentation ethanol production. The results showed that the pretreated water hyacinth fermented by the K. marxianus K213, Ogataea sp. WXT3, K.marxianus S16and S.cerevisiae. In the SHF fermentation show that K. marxianus K213, Ogataea sp. WXT3, K.marxianus S16, and S.cerevisiae strains consumed20.33g/l,20.81g/1,20.39g/l and20.33g/l of glucose hydrolyzate was used as substrate, respectively, and yields6.41g/l,5.99g/l,6.31g/1and7.10g/1of ethanol, respectively. Conversion rates of each strain were0.32g/g,0.29g/g,0.31g/g and0.35g/g, respectively. These data were61.8%,56.4%,60.7%and68.5%of the theoretical conversion rate, respectively. In the SSF fermentation, and their maximum ethanol the yield was7.34g/1,6.89g/l,7.89g/l and4.94g/l, respectively, compared to the separate hydrolysis and fermentation ethanol production were increased by14.5%,15.0%,25.0%, respectively. But, the S.cerevisiae of ethanol production significantly reduced. On comparisons, in the present study, K. marxianus S16as fermentation strains have more advantades in the conversion of pretreated bagasse and water hyacinth into ethanol.Two pre-processing methods improve the enzymatic hydrolysis rate of bagasse and water hyacinth. Especially in combination with H2O2alkali pretreatment of lignocellulose hydrolysis rate enhanced significantly, and has a great advantage under the mild experimental conditions. Meanwhile, in the SSF fermentation, ethanol production of three thermophile strain was significantly higher than that of S. cerevisiae. Particularly, K. marxianus S16strain is prominent, and the highest yield of ethanol were2.22times and1.60times higher than S. cerevisiae for bagasse and water hyacinth as a substrate in the SSF fermentation. This result reflects the advantages of thermophile strain in SSF ethanol fermentation. The results of this study can provide help and support to improve the pretreatment and fermentation of lignocellulosic ethanol production process. |
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