Optimization of carbohydrate productivity of Spirulina microalgae as a potential feedstock for bioethanol production

The main goal of this research is to use the biomass productivity, carbohydrate content, and carbohydrate productivity as useful responses for optimization of macronutrients concentrations (K2HPO4, NaHCO3, and NaNO3) in cultivation of Spirulina microalgae as a feedstock for bioethanol production. In this study, individual and synergistic effects of medium components on the mentioned responses were investigated. The culture medium was optimized using central composite design for achieving the maximize biomass productivity (165 mg L−1  day−1 at K2HPO4: 438 mg L−1, NaHCO3: 15.92 g L−1, and NaNO3: 0.5 g L−1), carbohydrate content (42.0% of dry mass at K2HPO4: 192 mg L−1, NaHCO3: 5.71 g L−1, and NaNO3: 0.63 g L−1), and finally carbohydrate productivity (56.97 mg L−1 day−1 at K2HPO4: 359 mg L−1, NaHCO3: 9.80 g L−1, and NaNO3: 0.60 g L−1). The most significant factors on the biomass productivity and carbohydrate productivity were K2HPO4 and NaHCO3. On the other hand, NaHCO3 was the most effective factor on the carbohydrate content. The results showed a significant interaction between K2HPO4 and NaNO3 (p value < 0.05) on the biomass productivity and carbohydrate productivity. In addition, the model revealed a significant interaction between K2HPO4 and NaHCO3 on the carbohydrate content. The concentrations of NaNO3 and NaHCO3 in modified medium were remarkably lower than those in Zarrouk medium. Some possible metabolic pathways causing these effects and interactions were discussed.