Department of Chemical Engineering, Lund University, P,O, Box 124, SE-221 00 Lund, Sweden.
Biotechnol Biofuels. 2013 Nov 29;6(1):169. doi: 10.1186/1754-6834-6-169.
Integration of second-generation (2G) bioethanol production with existing first-generation (1G) production may facilitate commercial production of ethanol from cellulosic material. Since 2G hydrolysates have a low sugar concentration and 1G streams often have to be diluted prior to fermentation, mixing of streams is beneficial. Improved ethanol concentrations in the 2G production process lowers energy demand in distillation, improves overall energy efficiency and thus lower production cost. There is also a potential to reach higher ethanol yields, which is required in economically feasible ethanol production. Integrated process scenarios with addition of saccharified wheat meal (SWM) or fermented wheat meal (FWM) were investigated in simultaneous saccharification and (co-)fermentation (SSF or SSCF) of steam-pretreated wheat straw, while the possibility of recovering the valuable protein-rich fibre residue from the wheat was also studied.
The addition of SWM to SSF of steam-pretreated wheat straw, using commercially used dried baker's yeast, S. cerevisiae, resulted in ethanol concentrations of about 60 g/L, equivalent to ethanol yields of about 90% of the theoretical. The addition of FWM in batch mode SSF was toxic to baker's yeast, due to the ethanol content of FWM, resulting in a very low yield and high accumulation of glucose. The addition of FWM in fed-batch mode still caused a slight accumulation of glucose, but the ethanol concentration was fairly high, 51.2 g/L, corresponding to an ethanol yield of 90%, based on the amount of glucose added.In batch mode of SSCF using the xylose-fermenting, genetically modified S. cerevisiae strain KE6-12, no improvement was observed in ethanol yield or concentration, compared with baker's yeast, despite the increased xylose utilization, probably due to the considerable increase in glycerol production. A slight increase in xylose consumption was seen when glucose from SWM was fed at a low feed rate, after 48 hours, compared with batch SSCF. However, the ethanol yield and concentration remained in the same range as in batch mode.
Ethanol concentrations of about 6% (w/v) were obtained, which will result in a significant reduction in the cost of downstream processing, compared with SSF of the lignocellulosic substrate alone. As an additional benefit, it is also possible to recover the protein-rich residue from the SWM in the process configurations presented, providing a valuable co-product.
将第二代（2G）生物乙醇生产与现有的第一代（1G）生产相结合，可能有助于从纤维素材料中商业化生产乙醇。由于 2G 水解物的糖浓度较低，并且在发酵前通常需要稀释 1G 流，因此混合流是有益的。在 2G 生产过程中提高乙醇浓度可以降低蒸馏过程中的能源需求，提高整体能源效率，从而降低生产成本。还有可能达到更高的乙醇产量，这是经济可行的乙醇生产所必需的。在蒸汽预处理的小麦秸秆的同步糖化和（共）发酵（SSF 或 SSCF）中，研究了添加糖化小麦粉（SWM）或发酵小麦粉（FWM）的集成工艺方案，同时还研究了从小麦中回收有价值的富含蛋白质纤维残渣的可能性。
使用商业上使用的干面包酵母酿酒酵母（Saccharomyces cerevisiae），将 SWM 添加到 SSF 蒸汽预处理的小麦秸秆中，可获得约 60g/L 的乙醇浓度，相当于约 90%的理论乙醇收率。由于 FWM 的乙醇含量，在分批 SSF 中添加 FWM 对面包酵母有毒，导致产量非常低，葡萄糖大量积累。在分批补料 SSF 中添加 FWM 仍会导致葡萄糖略有积累，但乙醇浓度相当高，为 51.2g/L，相当于基于添加的葡萄糖量，乙醇收率为 90%。在使用木糖发酵的遗传修饰酿酒酵母菌株 KE6-12 的 SSCF 分批模式下，与面包酵母相比，乙醇产量或浓度没有提高，尽管木糖利用率增加，但由于甘油产量的大幅增加，可能是由于甘油产量的大幅增加。与分批 SSCF 相比，在 48 小时后，以低进料速率向 SWM 中添加葡萄糖时，观察到木糖消耗略有增加。然而，乙醇产量和浓度仍保持在相同范围内。
与单独进行木质纤维素底物的 SSF 相比，获得了约 6%（w/v）的乙醇浓度，这将显著降低下游加工成本。作为额外的好处，也有可能从所提出的工艺配置中回收 SWM 中的富含蛋白质的残留物，提供有价值的副产物。
