Assessment of light distribution model for marine red microalga Porphyridium purpureum for sustainable production in photobioreactor

Microalgae can accumulate large amounts of nutrients from sustainable elements cycling and wastewater reuse. Light is a key factor determining productivity of algal biomass when recycling. However, light is unevenly distributed in photobioreactors due to light absorption and scatter by algal cells. Understanding the laws of light distribution is needed for optimizing the culture process. In this study, a light distribution model for red alga Porphyridium purpureum was used to optimize the cultivation process and improve culture performance by controlling light intensity. Compared to the Lambert-Beer model, the Hyperbolic law is more flexible and is applicable in a larger range of cell densities. In addition, the content of intracellular phycobiliprotein has a great influence on light distribution inside the photobioreactor while a higher biomass concentration reduces its impact. A maximum biomass concentration of 24.7 g/L along with 1.2 g/L/d cell growth rate was achieved by increasing incident light intensity in a stepwise fashion. The overall light conditions inside the photobioreactor during the culture process was also analyzed and discussed based on light distribution models. A volume-averaged light intensity regulated at ~50 μmol/m2/s along with an incident light intensity of less than 540 μmol/m2/s is an appropriate light condition for Porphyridium purpureum culture. The outcomes of light distribution model assessment and stepwise fashion regulation strategy can be applied to red microalgae in general, especially for high cell density cultivation. These findings provide an essential base for culture optimization, which can be used in future industrial applications of P. purpureum for water clean and sustainability of human nourishment production.