Continuous cultivation of photosynthetic microorganisms: Approaches, applications and future trends

Abstract

The possibility of using photosynthetic microorganisms, such as cyanobacteria and microalgae, for converting light and carbon dioxide into valuable biochemical products has raised the need for new cost-efficient processes ensuring a constant product quality. Food, feed, biofuels, cosmetics and pharmaceutics are among the sectors that can profit from the application of photosynthetic microorganisms. Biomass growth in a photobioreactor is a complex process influenced by multiple parameters, such as photosynthetic light capture and attenuation, nutrient uptake, photobioreactor hydrodynamics and gas-liquid mass transfer. In order to optimize productivity while keeping a standard product quality, a permanent control of the main cultivation parameters is necessary, where the continuous cultivation has shown to be the best option. However it is of utmost importance to recognize the singularity of continuous cultivation of cyanobacteria and microalgae due to their dependence on light availability and intensity. In this sense, this review provides comprehensive information on recent breakthroughs and possible future trends regarding technological and process improvements in continuous cultivation systems of microalgae and cyanobacteria, that will directly affect cost-effectiveness and product quality standardization. An overview of the various applications, techniques and equipment (with special emphasis on photobioreactors) in continuous cultivation of microalgae and cyanobacteria are presented. Additionally, mathematical modeling, feasibility, economics as well as the applicability of continuous cultivation into large-scale operation, are discussed.

Cyanobacterial metabolites as a source of sunscreens and moisturizers: a comparison with current synthetic compounds

“…On-going research into the intensive cultivation of photosynthetic microorganisms in photobioreactors such as the tubular system shown in Fig. 6, is bringing new understanding in terms of design, operation and scaleup (Fernandes et al, 2015), and will steadily improve both the economics and feasibility of industrial production of cyanobacteria. Furthermore, the discovery and characterization of superior cyanobacterial strains from the environment, together with their domestication and metabolic improvement using modern genetic engineering approaches (Lai & Lan, 2015), have the potential to bring significant improvements in productivity.…”

Nutrient removal from an anaerobic membrane bioreactor effluent using microalgae. Study and modeling of the process.

“…It has been reported that, theoretically, productivity in continuous cultivation systems is two to five times higher than that of batch systems (Fernandes et al, 2015). Operating in continuous mode enables the achievement of higher cell densities, which in turn also reduces harvesting costs.…”

“…This can be fought by increasing turbulence or manual or mechanical wall scraping. It is still necessary to provide demonstrative case studies which prove the advantages of continuous cultivation and allow a rigorous and realistic techno-economic assessment (Fernandes et al, 2015).For productivity maximization and product quality, permanent control of cultivation parameters is necessary. In the case of continuous cultivation, especially outdoors, it is essential to monitor the parameters by sensors and to know in advance the behavior of the microalgae under the cultivation conditions.…”

“…As an example of efforts made to overcome the problem of light variability, Mairet et al (2015) developed a static and an adaptive controller in order to regulate the light attenuation factor by changing the dilution rate, and thus optimize algal productivity. Generally, for a proper control of the process, information about optimal growth conditions and basic performance of the culture should be previously collected.Biomass growth and composition models should be then developed, since models are essential for monitoring and control (Fernandes et al, 2015). Naturally, the same applies regarding water quality in the case of microalgal cultivation for wastewater nutrient removal.…”

“…Biomass growth and composition models should be then developed, since models are essential for monitoring and control (Fernandes et al, 2015). Naturally, the same applies regarding water quality in the case of microalgal cultivation for wastewater nutrient removal.…”