Ha Jiyeon, Engler Cady R, Lee Seung Jae
Samsung Engineering Co. Ltd., R&D Center, Seoul, Republic of Korea.
Biotechnol Bioeng. 2008 Jul 1;100(4):698-706. doi: 10.1002/bit.21761.
Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited.
研究了百治磷和二乙基硫代磷酸酯（DETP）在海藻酸钙凝胶珠中的扩散特性，以辅助生物反应器系统的设计和运行。在适合生物降解研究的条件下测定的百治磷和DETP在海藻酸钙凝胶珠中的扩散系数分别为2.70×10⁻¹¹ m²/s和4.28×10⁻¹¹ m²/s。百治磷和DETP的扩散率受几个因素影响，包括本体溶液的粘度、搅拌速度以及扩散底物和固定化细胞的浓度。扩散系数随搅拌速度的增加而增大，这可能是由于低速时混合不佳以及高速时珠子的一些磨损所致。扩散系数也随底物浓度的降低而增大。凝胶珠中细胞浓度的增加导致扩散率降低。预测扩散率作为细胞重量分数函数的理论模型高估了百治磷和DETP的有效扩散率，但有效扩散率与细胞重量分数之间的线性关系是从实验数据得出的。本研究中使用的半径为1.65 - 1.70 mm的海藻酸钙凝胶珠不存在扩散限制：基于毕奥数计算，外部传质阻力可忽略不计，有效因子表明内部传质阻力也可忽略不计。因此，海藻酸钙凝胶珠内部百治磷和DETP的降解速率受反应限制。
