高浓度酒精连续发酵过程中振荡行为的模拟及填料弱化振荡的机理

在利用酿酒酵母进行高浓度酒精连续发酵中，观察到了一种持久稳定的振荡现象，表现为当严格控制发酵参数时，发酵罐中残糖浓度、酒精浓度和生物量浓度呈现大幅度的周期性波动。前期研究工作推测，细胞对环境胁迫的延迟反应是引起这种振荡行为的主要原因之一，并发现填料具有弱化这种振荡行为的作用，但描述这种振荡行为的动态模型尚未建立，填料弱化振荡的机理也尚不清楚。通过引入时滞加权函数，建立了预测高浓度发酵（VHGF）条件下振荡行为的过程动态模型。并在前期实验研究基础上，分别采用3种性质不同的填料，通过考察其弱化振荡行为的差异，在一定程度上揭示填料对振荡行为弱化作用的机理。实验结果表明：采用木块填料能明显地弱化振荡现象，金属丝网环和聚氨酯填料则不能弱化振荡现象；填料弱化振荡现象的原因与酵母细胞生长微环境的改变有关；利用聚氨酯作为填料能显著提高反应器中的生物量浓度，从而显著提高反应器系统的设备生产强度指标。

Dynamic models of VHG continuous ethanol fermentation and mechanisms of oscillation attenuation by packing

Prior research reported the sustainable parameter oscillations characterized by long periods and high amplitudes in the continuous ethanol fermentation system when very high gravity(VHG) medium was fed.In this study, a bioreactor system composed of a continuous stirred tank reactor(CSTR) and three-stage tubular bioreactors in series was set up,and the dynamics of the oscillatory behavior in such a fermentation process was investigated by the weighting treatment of the specific growth rate of yeast cells, which considered the lag response of yeast cells to the stress exerted by the environment.Model parameters were estimated and validated by experimental data.Furthermore, the tubular bioreactors were packed with wood chip (5 mm×5 mm×5 mm),stainless steel net ring (10 mm×10 mm) and polyurethane (10 mm×10 mm×10 mm)respectively which were significantly different in their surface properties and corresponding yeast cell immobilization roles through adsorption.It was found that the wood chip was the best in attenuating the parameter oscillations although its yeast cell immobilization role was between the other two, which indicated that, in addition to the yeast cell immobilization, other factors also significantly contributed to the attenuation of the parameter oscillations.Further investigations revealed that the micro-environmental changes of the tubular bioreactors created by these different packings which inevitably changed the specific growth rate of the yeast cells as well as the dilution rate changes correspondingly after the tubular bioreactors were packed and their working volumes decreased, also contributed to the attenuation of the parameter oscillations.The polyurethane packings showed the best immobilization performance, which increased the biomass concentration and consequently the productivity significantly.