Kinetic modeling of microalgae growth and CO₂ bio-fixation using central composite design statistical approach

The optimum growth (μ), CO₂ bio-fixation (R_CO) rates and the energy ratio (ER) of microalgae Chlorella vulgaris (C.v) were identified using central composite design statistical approach (CCD-SA). μ and R_CO parameters including temperature of photobioreactor (T_PBR), concentration of CO₂ (C_CO ), nutrients (carbon, nitrogen and phosphorus), gas flow rate (Q_gas), initial inoculum concentration (IN_den) and the solar light intensity (I_tot) were considered. Results revealed mild operational conditions in the range 20-25 °C, C_CO of 2.5-20% (v/v), Q_gas of 0.5-0.8 vvm and I_tot of 50-200 μE/m²·s would generate considerable μ and R_CO. The highest μ and R_CO with a significant ER of 19.5 were generated under CCD-SA optimized parameters of T = 25 °C, C_CO = 20%, Q_gas = 0.5 ± 0.05 (Std. Dev. = 0.04) vvm, total inorganic nitrogen (TN) = 19 ± 2 (Std. Dev. = 0.1) mg-N/L, Total phosphorous = 7 ± 1 (Std. Dev. = 0.7) mg-P/L, COD = 20 ± 2 (Std. Dev. = 0.5) mg-COD/L, IN_den = 0.52 ± 0.01 (Std. Dev. = 0.05) mg/L and I_tot = 150 ± 2(Std. Dev. = 0.6) μE/m²s). Microalgae technology can be considered as a promising technology for CO₂ bio-fixation in a large scale with a sustainable value of the produced biomass for biofuel production.