Photobioreactors

Photobioreactors (PBRs) have a major role in cultivating phototrophic microorganisms to fix CO₂ and produce target products. Light penetration and distribution as the energy source and the supply of CO₂ as the inorganic carbon source are the two key factors for PBR design. Among phototrophic microorganisms grown in PBRs, microalgae are the most popular ones with high potential for commercial applications, because they are considered third-generation feedstock for the production of biofuels and bio-based chemicals. Therefore, this chapter focuses on describing the effects of PBR design and operation on the cultivation of microalgae. Conventionally, microalgae are cultured in open pond systems, which are cost-effective, but they have obvious disadvantages such as poor mass transfer efficiency and the high possibility of contamination. Closed-type PBRs are generally not economic owing to high installation and maintenance costs, but they are more efficient in terms of light and gas distribution when they are appropriately designed and operated. Low-cost, energy-efficient PBRs with properly controlled systems to monitor the performance of the algal culture are the ultimate goal in large-scale or industrial-scale algal cultivation. In this chapter, factors affecting microalgal growth and photosynthesis and how this knowledge can be useful in designing efficient PBRs are discussed. Various types of PBRs are introduced with an emphasis on closed-type systems. Factors to be considered for microalgal cultivation in PBRs with different configuration are also discussed. Finally, commercial microalgae cultivation systems currently in use and applications of the obtained microalgal biomass are reviewed.