Using non-metric multi-dimensional scaling analysis and multi-objective optimization to evaluate green algae for production of proteins, carbohydrates, lipids, and simultaneously fix carbon dioxide

Eight green-algae species were investigated to elucidate the effects of growth phases on biomass productivity (CO₂ fixation rate) and accumulation of algal macromolecules (proteins, carbohydrates, and lipids). Non-metric multi-dimensional scaling (NMDS) and multiple-objective optimization were applied to evaluate the effects of algal species and growth phases on biomass productivity and algal macromolecule accumulation. Algal species and growth phases had significant impacts on biomass production and composition. NMDS delineated that biomass productivity and protein accumulation of all species were dominant in the log phase, while the stationary phase was favorable for lipid and carbohydrate accumulation. Among the eight algal species, Chlorella vulgaris had the highest biomass productivity (75 mg/L/day) and a high protein content in the exponential phase (53%). Scenedesmus obliquus had the highest protein content (55%) in the log phase, Botryococcus braunii showed the highest lipid content (40%) in the stationary phase, and Staurastrum sp. presented the highest carbohydrate content (37%) in the stationary phase. Two-objective optimization for algal biomass productivity and composition led to the conclusion that Chlorella vulgaris, Botryococcus braunii, and Coelastrum microporum are the preferred strains for accumulation of proteins, lipids, and carbohydrates, respectively, along with good CO₂ fixation (biomass productivity). NMDS and multi-objective optimization are useful tools to select preferred strains and corresponding culture conditions from a large pool of candidates for simultaneous biomass and macromolecule accumulation.