自絮凝酵母高浓度重复批次乙醇发酵

Consecutive very-high-gravity batch ethanol fermentation with self-flocculation yeast

摘要:

利用发酵性能优良的自絮凝酵母Saccharomyces cerevisiae flo, 研究开发了重复批次高浓度乙醇发酵系统, 以节省下游加工过程的能耗。在终点乙醇浓度达到120 g/L左右的条件下, 发酵系统的乙醇生产强度达到8.2 g/(L·h)。然而实验中发现, 随着发酵批次的增多, 自絮凝酵母沉降性能逐渐下降, 从发酵液中沉降分离所需时间相应延长, 导致发酵液中高浓度乙醇对酵母的毒害作用加剧, 影响其发酵活性和发酵系统运行的稳定性，发酵装置运行11个批次后无法继续运行。实验结果表明，絮凝能力下降导致的酵母絮凝颗粒尺度减小是其沉降性能下降的主要原因。进一步研究发现, 酵母的絮凝能力通过再培养可以恢复。在此基础上对发酵系统操作进行改进, 每批发酵结束后可控采出一定比例菌体, 调节系统的酵母细胞密度和乙醇生产强度以刺激酵母增殖, 保持其絮凝能力。在达到相同发酵终点乙醇浓度条件下, 虽然发酵系统的乙醇生产强度降低到4.0 g/(L·h)，但运行10 d后絮凝颗粒酵母尺度趋于稳定，继续运行14 d, 未发现絮凝颗粒酵母尺度继续下降的现象，系统可以稳定运行。

Abstract:

In order to save energy consumption for the downstream processes, consecutive very-high-gravity batch fermentation was developed for ethanol production with the self-flocculating yeast Saccharomyces cerevisiae flo. The fermentation system exhibited a high ethanol productivity of 8.2 g/(L·h) with average ethanol concentration around 120 g/L. However, deterioration of the sedimentation performance of yeast flocs was observed as the consecutive fermentation process was prolonged, which significantly extended the time required for yeast flocs to separate from fermentation broth, and exaggerated the inhibition of high ethanol concentration on the yeast flocs, making them quickly lost viability and the fermentation system interrupted after 11 consecutive batches. Experimental results illustrated that decrease of the size of yeast flocs was the main reason, which could be prevented by stimulating the propagation of the yeast flocs. Thus, yeast was purged from the fermentation system at the end of each batch, and the concentration of yeast flocs within the fermentor was maintained at a relatively low level to stimulate their propagation. Although the ethanol productivity was decreased to 4.0 g/(L·h), the size of yeast flocs was stabilized after 10 consecutive batches and maintained for another 14 batches without further decrease, indicating the fermentation system could be operated reliably.