Photobioreactor cultivation strategies for microalgae and cyanobacteria

Abstract

The current burden on fossil-derived chemicals and fuels combined with the rapidly increasing global population has led to a crucial need to develop renewable and sustainable sources of chemicals and biofuels. Photoautotrophic microorganisms, including cyanobacteria and microalgae, have garnered a great deal of attention for their capability to produce these chemicals from carbon dioxide, mineralized water, and solar energy. While there have been substantial amounts of research directed at scaling-up production from these microorganisms, several factors have proven difficult to overcome, including high costs associated with cultivation, photobioreactor construction, and artificial lighting. Decreasing these costs will substantially increase the economic feasibility of these production processes. Thus, the purpose of this review is to describe various photobioreactor designs, and then provide an overview on lighting systems, mixing, gas transfer, and the hydrodynamics of bubbles. These factors must be considered when the goal of a production process is economic feasibility. Targets for improving microalgae and cyanobacteria cultivation media, including water reduction strategies will also be described. As fossil fuel reserves continue to be depleted and the world population continues to increase, it is imperative that renewable chemical and biofuel production processes be developed toward becoming economically feasible. Thus, it is essential that future research is directed toward improving these processes. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:811-827, 2018.

Non‐endogenous ketocarotenoid accumulation in engineeredSynechocystissp. PCC 6803

“…These properties, their rather plane growth requirements and the already established genetic tools for their metabolic engineering, make cyanobacteria one of the most appealing class of phototrophic organisms to be employed for biotechnological applications (Knoot et al ). However, several hurdles have to be overcome in order to render the industrial exploitation of cyanobacteria economically feasible (Johnson et al ). A promising strategy to increase the cost‐effectiveness of cyanobacteria cultivation plants may consist of coupling the production of biofuels with one of the added‐value molecules, such as carotenoids.…”

Production and Use of Sustainable C2‐C4 Alcohols – An Industrial Perspective

“…A further aspect that needs to be taken into account is the risk of releasing GMOs into the atmosphere. Although research is underway to overcome the obstacles associated with this approach [73][74][75] through genetically engineering organisms and developing advanced photobioreactor designs, no commercial success has yet been observed for the production of C2-C4 alcohols [71,75].…”

Evaluation of New Genetic Toolkits and Their Role for Ethanol Production in Cyanobacteria

“…Alternatively, for some heterotrophic cyanobacteria, like Synechocystis, the addition of an organic carbon source in the dark phase could prevent the product degradation, whereby again the cultivation costs would increase [23]. For the overall cost-efficient large-scale production, the design of a photobioreactor and the general production process has to be optimized for the ethanol production, which includes the possibilities for downstream processing [25,26]. Since ethanol is secreted from all described organisms, costly cell disruption methods are not needed and, due to its volatility, it can be harvested within a distillation process [20,22].…”