甜高粱茎汁及茎渣同步糖化发酵工艺优化

为了提高甜高粱秸秆乙醇生产中茎汁和茎渣的利用,以甜高粱茎汁及其渣为发酵原料,对茎汁茎渣混合原料同步糖化乙醇发酵的工艺条件进行优化研究。采用Plackett-Burman(PB)筛选设计试验筛选出影响甜高粱茎秆渣汁同步糖化乙醇发酵的显著因素。采用响应面法建立了同步糖化发酵乙醇生产的乙醇产量数学模型。根据该模型进行了工艺参数的优化,以乙醇产量为指标,试验所得甜高粱茎秆渣汁同步糖化化乙醇发酵的优化工艺条件为:发酵温度36.58℃,混合纤维素酶添加量=23.5(FBU/m L)/35.25(CBU/m L),甜高粱渣汁质量体积比为8.2%,理论预测乙醇产量为89.2%,在此条件下进行验证试验,乙醇产量为88.98%,平均质量浓度,验证了数学模型的有效性,为提高甜高粱茎汁及茎渣混合原料同步糖化发酵产乙醇和提高发酵效率提供参考。

Optimization of ethanol production from bagasse and juice of sweet sorghum stem by simultaneous saccharification and fermentation

Ethanol production from energy crops which are renewable resources has gotten more and more attentions because of the energy crisis and environmental pollution. Sweetsorghum is considered as the most promising energy crop for the production of ethanol. Sweetsorghum stem is usually used to ferment ethanol, one of which is the liquid-state fermentation with the juice of sorghum stem. But a lot of bagasse of sorghum stem is discarded as wastes. The bagasse can be used as the supplemental materials of the fermentation of the juice. So it is absolutely necessary to study on the optimization of ethanol production with the bagasse and juice of the sorghum stem by simultaneous saccharification and fermentation (SSF). The response surface is an effective method to optimize the operating parameters of the SSF for the maximum ethanol yield. In this study, the Plackett-burman design was adopted to select the significant factors from 8 variables which influenced the ethanol yield and its concentration. The results indicated the ethanol yield and concentration were mainly influenced by the fermentation temperature, the amount of cellulase and the ratio of sorghum stem bagasse to its juice (P<0.05). And the other 5 variables which were not significant were remained to be the center level: the pH value was 5.5, the inoculation ratio was 0.2%, the amount of (NH4)2SO4 was 5 g/L, the fermentation time was 60 h, and the amount of uracil was 1 g/L. Based on the results of the selection, the steepest ascent experiment was conducted to determine the center point and the step size. The center point of the fermentation temperature was 37℃ and its step size was 3℃. The center point of the amount of cellulase was 20 FBU/30 CBU and its step size was 5 FBU/CBU. The center point of the ratio of bagasse to its juice was 7% and its step size was 1.5%. Then we adopted the Box-Behnken design and response surface analysis method to optimize the levels of these 3 significant factors, and the regression and the optimal levels of these significant factors were as follows: the regression model was very significant (P<0.0001,R2=0.9987, Adj.R2=0.9971 andCV=0.0099), which indicated that the model was reliable, and therefore, the regression model could be used for the theoretical prediction of the SSF for juice and bagasse of sweet sorghum stem; the fermentation temperature was 36.58℃, the amount of cellulase was 23.5 FBU/35.25 CBU, the ratio of bagasse to juice of sorghum stem was 8.2%, the maximum theoretical yield of ethanol predicted was 89.2%, and the ethanol concentration was 31.829 g/L. The interactive effects were analyzed by response surface analysis. The interactive effect of the fermentation temperature and the amount of cellulase was very significant (P<0.0001); the interactive effect of the amount of cellulase and the ratio of bagasse to juice was very significant (P<0.001); the interactive effect of the fermentation temperature and the ratio of bagasse to juice was not significant (P=0.2946). Under the optimal conditions, the model was proved to be valid by the verification test with 3 repeated tests, and the ethanol yield was 88.98% which was very close to the maximum yield (89.2%). The ethanol concentration was 31.78 g/L, which was very close to theoretical prediction value (31.829 g/L). The results of this optimal technology will provide a reference for the ethanol production technology by simultaneous saccharification and fermentation method for sweet sorghum stem.