Biophotonics for improving algal photobioreactor performance: A review

The use of algae as a feedstock for biofuels production has drawn considerable attention due to their high biomass yield, their ability to be cultivated using degraded water on nonarable land, and their ability to recover nutrients from wastewater. Although algae have the potential to provide biomass for biofuels, some challenges remain and the limitations may be overcome by improving algal growth rates together with lipid synthesis. To achieve this, scientific researchers have focused on isolating and screening algal strains with better growth rates and lipid synthesis capabilities, bioengineering, and optimizing culture systems. The present review focuses on the biophotonic-based manipulations that can be applied to optimize solar-powered photobioreactors (PBRs). Hence, three different types of solar filters are reviewed herein, that is, the colored glass, thin-film, and thermochromic filters. This review provides evidence that bright red-colored glass filters can lower the spectral intensity of solar radiation from 1982.13 to 393.71 mu mol m(-2) s(-1), which is preferable for improved biomass productivity. Changing filter color, once the desired biomass concentration has been amassed, to medium blue or bright pink further improves lipid yield. A 34% improvement in biomass productivity was observed for Chlorella vulgaris cultured under thin-film filters. Thin-film filters are also effective in regulating PBR temperature within the 24-31 degrees C range, which is tolerable for most algal species. Furthermore, this study highlights that the applicability of thermochromic filters in PBR designs is still yet to be investigated. Thermochromic filters are reflective and absorptive under high and low temperatures, respectively, a technology that can be a solution to the overheating challenge of PBRs. This review recommends the coupling of these light filtration technologies to the horizontal tubular PBR for effective utilization of solar radiation in algaculture.