自絮凝颗粒酵母表观生长动力学

Development of observed kinetic model for self-flocculating yeast

首先利用激光聚焦反射颗粒测量系统在线监测了自絮凝颗粒酵母粒径分布,通过提高发酵罐搅拌速率减小了颗粒粒径,消除了内扩散影响,获得了本征动力学模型。进而基于颗粒内部薄壳物料衡算理论,建立了表观动力学模型,并通过不同底物浓度和自絮凝酵母颗粒粒径分布条件下发酵实验数据拟合,获得了模型的参数。在此基础上,分析了内扩散效应导致颗粒内部可能出现死区的影响,绘制了发酵培养基初始糖和自絮凝颗粒酵母粒径影响的操作图,分析了这一发酵体系的性能。结果表明对于工业生产中普遍采用的多级串联连续乙醇发酵系统,主发酵罐和后发酵罐由于残糖水平差别较大,使颗粒内部因底物枯竭而导致内扩散效应的可能性显著不同:主发酵罐适宜于较大粒径自絮凝颗粒酵母体系,以利于固定化,提高发酵罐中细胞密度和生产强度;而后发酵罐适宜于较小粒径自絮凝颗粒酵母,以减轻底物内扩散影响,保持所需的发酵活性。因此需要综合考虑工程操作和动力学行为,对自絮凝颗粒酵母粒径分布进行优化控制。

With on-line monitoring size distribution of the self-flocculating yeast with the focused beam reflectance measurement （FBRM） system, the impact of mass transfer limitation was eliminated by increasing stirring speed of the fermentor to reduce the size of yeast flocs, and an intrinsic kinetic model for yeast growth was established. Furthermore, based on the shell mass balance theory, an observed kinetic model was developed and model parameters were determined with experimental data collected under the condition of different substrate concentrations and yeast floc size distributions. The analytical results of yeast flocs kinetic behavior indicated that size distribution should be controlled properly in the tanks-in- series system for continuous ethanol fermentation. Large yeast floes were preferred for the main tanks where higher sugar concentrations could prevent the occurrence of mass transfer limitation, while small yeast floes should be used for the rear tanks to maintain yeast floes viability and fermentability in which sugar depletion significantly increased the risk of mass transfer limitation on yeast floes. The engineering aspects, such as separation of yeast flocs from the fermentation broth by sedimentation, effective immobilization of yeast floes within the fermentation system by retention and balancing size distributions.