Abstract
Photosynthetic microorganisms are important bioresources for producing desirable and environmentally benign products, and photobioreactors (PBRs) play important roles in these processes. Designing PBRs for photocatalysis is still challenging at present, and most reactors are designed and scaled up using semiempirical approaches. No appropriate types of PBRs are available for mass cultivation due to the reactors' high capital and operating costs and short lifespan, which are mainly due to a current lack of deep understanding of the coupling of light, hydrodynamics, mass transfer, and cell growth in efficient reactor design. This review provides a critical overview of the key parameters that influence the performance of the PBRs, including light, mixing, mass transfer, temperature, pH, and capital and operating costs. The lifespan and the costs of cleaning and temperature control are also emphasized for commercial exploitation. Four types of PBRs-tubular, plastic bag, column airlift, and flat-panel airlift reactors are recommended for large-scale operations. In addition, this paper elaborates the modeling of PBRs using the tools of computational fluid dynamics for rational design. It also analyzes the difficulties in the numerical simulation, and presents the prospect for mechanism-based models. (C) 2017 THE AUTHORS. Published by Elsevier LTD on behalf of the Chinese Academy of Engineering and Higher Education Press Limited Company.
Highlights
Even though tremendous progress has been achieved in simulating the bubbly flow in PBRs, some researchers still consider the computational fluid dynamics (CFD) simulation of this process to be more of an “art” than a “science” because of premature models related to the turbulence and interphase momentum exchange [45,102]
Photosynthesis works in the full range of irradiation wavelengths of the photosynthetically active radiation (PAR), and the absorption and scattering coefficients are spectral dependent, the solution to the radiative transfer equation (RTE) for a PBR is currently confined to pseudo-monochromatic radiation, and averaged radiation source and radiative properties are employed in the computation in order to reduce the huge computational cost
The mechanism-based photosynthetic factories” (PSFs) model described above takes into account the photoacclimation dynamics, the responses of overdose irradiation and dark respiration in the photolimitation zones, and the shear exerted on the cells
Summary
Photosynthetic microorganisms such as unicellular microalgae, cyanobacteria, and plant cells are high-potential bioresources that are promising for various applications, including valuable food and animal feed production [1,2], nutraceutics [3,4], pharmaceutics [5,6], pigments and cosmetics [5,7], wastewater treatment [8,9], fine chemicals [2,10] and biofuels [11,12], carbon dioxide (CO2) biosequestration [10,13], and so forth. The photobioreactor (PBR) process is designed to convert solar energy into desirable products It is a highly attractive approach compared with open-air systems [14], which use photosynthetic organisms, due to its favorable advantages such as higher photosynthetic efficiency, higher concentrations and areal productivities, low contamination, the prevention of water loss caused by evaporation, and a precisely controlled environment [13,15]. This work analyzes the effects of the principal factors on the performance of commercial PBRs, and summarizes the most promising PBRs for the large-scale commercial exploitation of microalgae. It elaborates theoretical models, which include the interplay among light, mixing, mass transfer, and cell growth, for the rational design of efficient PBRs. Further insight into the design of commercial PBRs for the mass cultivation of photosynthetic microorganisms is provided
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