Autotrophic cultivation of Spirulina platensis for CO2 fixation and phycocyanin production

Microalgae biotechnology provides a new industrial paradigm that simultaneously yields various vital products and captures CO2 in a single process. Development of optimal strategies to harness microalgal resources is critical to full-scale production and application of microalgae-derived products. This work parametrically investigated the autotrophic cultivation of Spirulina platensis for enhanced simultaneous CO2 fixation and phycocyanin production using conical flasks and newly designed photobioreactors. In the absence of culture aeration in the conical flasks, a maximum biomass concentration of 3.20 g/L was achieved under alkaline conditions with initial pH of ∼9. In the presence of culture aeration, a maximum biomass concentration of 5.96 g/L was obtained under intermittent CO2 supply at 20 mM/(L 2 d) (that is 20 mM/L every other day). Continuous sparging of 0.1 L/min compressed air in combination with 20 mM/(L d) intermittent CO2 supply into a customarily designed photobioreactor resulted in biomass and crude phycocyanin concentrations of 5.92 g/L and 1.06 g/L respectively. Further photobioreaction optimization resulted in biomass and phycocyanin concentrations of 7.27 g/L and 1.22 g/L respectively using 20 mM/L d CO2 intermittent aeration supplemented with continuously supplied compressed air under specific flow conditions. The highest volumetric titre of phycocyanin obtained in this work is amongst the highest reported in literature. These results indicate that high biomass, phycocyanin concentration and CO2 fixation rate could be obtained with minimal extra effort simply by optimizing bioprocess conditions. The growth results of S. platensis cultivation fitted well to the logistic rate equation.

► A novel low-cost photobioreactor suitable for microalgae autotrophic cultivation is developed.
► An effective experimental and mathematical interpretive system is applied to enhance microalgal cell growth and photosynthetic rates.
► Optimized bioprocess condition for the production of high phycocyanin volumetric titres from algal biomass is developed.