Potential CO₂ biofixation by microalgae strains for industrial application

CO₂ biofixation via microalgae is sustainable option for CO₂ capturing. In this work, CO₂ was directly supplied by the flue gas from Neka thermal power plant. The propagation of microalgal species including Spirulina Sp., Chlorella vulgaris and Scenedesmus obliquus were compared for their ability in CO₂ biofixation and accumulation of lipids in algal biomass at CO₂ concentrations of 0.03, 2 and 5%. The growth kinetic model for the projection of algal growth by two mathematical models, including logistic and Gompertz were employed to fit and validate obtained experimental data. For the three strains of microalgae, Gompertz model fits the growth curves of microalgae much better than logistic model. Based on obtained results, the growth rate of three strains of microalgae at the same conditions were compared. The maximum growth rate, biomass productivity (P_B), CO₂ consumption rate (P_CO2) and lipid content with 5% CO₂ for C. vulgaris were 0.44 d⁻¹, 169.75 mg L⁻¹ d⁻¹, 319 mg L⁻¹ d⁻¹ and 32.8%, respectively. Subsequently, response surface methodology (RSM) was employed for optimization of light intensity and pH to achieve the maximum biomass concentration of C. vulgaris through central composite design (CCD). At optimum cultivation conditions for C. vulgaris microalgae, the maximum biomass concentration was 1908 mg L⁻¹ at light intensity of 3200 lx and pH 8 with 5% CO₂. Bench-scale data were obtained for optimization conditions and cultivation of C. vulgaris microalgae by RSM. Based on optimum conditions, the obtained biomass concentration in the bench-scale photobioreactor was 4.71% higher than laboratory scale.