Dale M C, Chen C, Okos M R
Department of Agricultural Engineering, Purdue University, W. Lafayette, Indiana 47907, USA.
Biotechnol Bioeng. 1990 Dec 5;36(10):983-92. doi: 10.1002/bit.260361003.
The viable fraction of immobilized cells in a bioreactor may be critical in predicting long-term or steady-state reactor performance. The assumption of near 100% viable cells in a bioreactor may not be valid for portions of immobilized cell reactors (ICRs) characterized by conditions resulting in appreciable death rates. A mathematical model of an adsorbed cell type ICR is presented in which a steady-state viable cell fraction is predicted, based on the assumptions of no cell accumulation in the reactor and a random loss of cells from the reactor. Data on cell death rates, cell growth rates, and productivity rates as functions of temperature, substrate, and ethanol concentration for the lactose utilizing yeast K. fragillis were incorporated into this model. The steady-state reactor viable cell fraction as predicted by this model is a strong function of both temperature and ethanol concentration. For example, a stable 20% viable fraction of the immobilized cells is predicted in ICR locations experiencing continuous conditions of either 30 g/L ethanol at 40 degrees C, or 95 g/L ethanol at 25 degrees C. Steady-state ICR "plug flow" concentration profiles and column productivities are predicted at three operating temperatures, 20, 30, and 40 degrees C using two different models for ethanol inhibition of productivity. These profiles suggest that the reactor operating temperature should be low if higher outlet ethanol concentrations are desired. Three reactor design strategies are presented to maximize the viable cell fraction and improve long-term ethanol productivity in ICR's: (1) reducing outlet ethanol concentrations, (2) rotating segments of an ICR between high and low ethanol environments, and (3) simultaneous removal of the ethanol produced from the reactor as it is formed.
生物反应器中固定化细胞的存活分数对于预测长期或稳态反应器性能可能至关重要。对于某些固定化细胞反应器（ICR）部分而言，假设生物反应器中细胞存活率接近100%可能并不成立，这些部分的特征是存在导致明显死亡率的条件。本文提出了一种吸附细胞型ICR的数学模型，该模型基于反应器中无细胞积累以及细胞从反应器中随机损失的假设来预测稳态存活细胞分数。将利用乳糖的酵母脆壁克鲁维酵母的细胞死亡率、细胞生长率和生产率作为温度、底物和乙醇浓度的函数的数据纳入该模型。该模型预测的稳态反应器存活细胞分数是温度和乙醇浓度的强函数。例如，在40℃下30 g/L乙醇或25℃下95 g/L乙醇的连续条件下，预测ICR位置的固定化细胞稳定存活分数为20%。使用两种不同的乙醇抑制生产率模型，预测了在20、30和40℃三个操作温度下的稳态ICR“活塞流”浓度分布和柱生产率。这些分布表明，如果需要更高的出口乙醇浓度，反应器操作温度应较低。提出了三种反应器设计策略，以最大化存活细胞分数并提高ICR中的长期乙醇生产率：（1）降低出口乙醇浓度；（2）在高乙醇和低乙醇环境之间旋转ICR段；（3）在乙醇形成时同时从反应器中去除产生的乙醇。
