The Role of Photo-Cycles in the Modulation of Growth and Biochemical Profile of Microalgae: Part I—Food Interest Compounds

The Role of Light on the Microalgae Biotechnology: Fundamentals, Technological Approaches, and Sustainability Issues

Light energy directly affects microalgae growth and productivity. Microalgae in natural environments receive light through solar fluxes, and their duration and distribution are highly variable over time. Consequently, microalgae must adjust their photosynthetic processes to avoid photo limitation and photoinhibition and maximize yield. Considering these circumstances, adjusting light capture through artificial lighting in the main culture systems benefits microalgae growth and induces the production of commercially important compounds. In this sense, this review provides a comprehensive study of the role of light in microalgae biotechnology. For this, we present the main fundamentals and reactions of metabolism and metabolic alternatives to regulate photosynthetic conversion in microalgae cells. Light conversions based on natural and artificial systems are compared, mainly demonstrating the impact of solar radiation on natural systems and lighting devices, spectral compositions, periodic modulations, and light fluxes when using artificial lighting systems. The most commonly used photobioreactor design and performance are shown herein, in addition to a more detailed discussion of light-dependent approaches in these photobioreactors. In addition, we present the principal advances in photobioreactor projects, focusing on lighting, through a patent-based analysis to map technological trends. Lastly, sustainability and economic issues in commercializing microalgae products were presented.

Growth Efficiency of Chlorella sorokiniana in Synthetic Media and Unsterilized Domestic Wastewater

Incorporating a variety of microalgae into wastewater treatment is considered an economically viable and environmentally sound strategy. The present work assessed the growth characteristics of Chlorella sorokiniana during cultivation in balanced synthetic media and domestic wastewater. Increasing the NH4+-N concentration to 360 mg L-1 and adding extra PO43--P and SO42--S (up to 80 and 36 mg L-1, respectively) contributed to an increase in the total biomass levels (5.7-5.9 g L-1) during the cultivation of C. sorokiniana in synthetic media. Under these conditions, the maximum concentrations of chlorophylls and carotenoids were 180 ± 7.5 and 26 ± 1.4 mg L-1, respectively. Furthermore, when studying three types of domestic wastewaters, it was noted that only one wastewater contributed to the productive growth of C. sorokiniana, but all wastewaters stimulated an increased accumulation of protein. Finally, the alga, when growing in optimal unsterilized wastewater, showed a maximum specific growth rate of 0.73 day-1, a biomass productivity of 0.21 g L-1 day-1, and 100% NH4+-N removal. These results demonstrate that the tested alga actively adapts to changes in the composition of the growth medium and accumulates high levels of protein in systems with poor-quality water.