Abstract

An enclosed air-lift photobioreactor (ALPBR) is considered an efficient lab-scale bioreactor for microalgae cell growth and lipid biosynthesis. However, fluid-induced shear stress and mixing are two main factors that affect physiological metabolism in microalgal cell cultures. Herein, a 50-L ALPBR after being designed and manufactured was evaluated for microalgal suspension culture. Moreover, computational fluid dynamics (CFD) simulation was used to characterize the hydrodynamics of ALPBR. Specifically, two model microalgae species Chlorella vulgaris and Chlorella protothecoides were cultured with aeration rates at 0.1, 0.2, 0.3, 0.4 volume per volume per minute (vvm). The hydrodynamics of ALPBR while considering shear rate, volume average velocity, turbulent energy dissipation rate (EDR), air volume fraction, and mean air bubble diameter, etc. showed that aeration generated a very low shear stress. When C. protothecoides and C. vulgaris were cultured with various aeration rates, the maximum dry cell weights (DCW) of two microalgal species tested were 0.3 vvm and 0.2 vvm, while the maximum lipid contents of both species were about 15.0% of the DCW, which were achieved at an air flow rate of 0.2 vvm. Therefore, we concluded that the shear rate generated by aeration could play a vital role in the cell growth of microalgae grown in an air-lift photobioreactor.

摘要

封闭式气举光生物反应器（ALPBR）被认为是用于微藻细胞生长和脂质生物合成的高效实验室规模的生物反应器。然而，流体诱导的剪切应力和混合是影响微藻细胞培养物中生理代谢的两个主要因素。在此，对设计和制造后的50L ALPBR进行微藻悬浮培养的评价。此外，使用计算流体动力学（CFD）模拟来表征ALPBR的流体动力学。具体来说，两种典型的微藻物种小球藻（Chlorella vulgaris）和原球藻（Chlorella protothecoides）以每分钟每体积（vvm）的0.1、0.2、0.3、0.4体积的曝气速率进行培养。ALPBR的流体动力学特性同时考虑了剪切速率，体积平均速度，湍流能量耗散率（EDR），空气体积分数和平均气泡直径等。表明曝气产生了非常低的剪切应力。当C. protothecoides和C.寻常以不同的通气速率进行培养，测试的两种微藻物种的最大干细胞重量（DCW）分别为0.3 vvm和0.2 vvm，而两种物种的最大脂质含量约为DCW的15.0％，这是在空气流下实现的速率为0.2 vvm。因此，我们得出结论，通气产生的剪切速率可能在气举光生物反应器中生长的微藻细胞的生长中起着至关重要的作用。