Optimization of microalgal biomass and lipid productivities for bioenergy production using central composite design with desirability function

This study investigates the influences of light-dark cycles and NaNO₃ dose on Chlorella kessleri microalgal-specific growth rate (SGR), biomass productivity (P), and intracellular lipid productivity (LP) by using central composite design with desirability function. A single-objective optimization showed that the maximum SGR, P, and LP can be achieved as 0.487 day⁻¹, 58.718 g/L day⁻¹, and 14.252 mg/L day⁻¹, respectively. The corresponding optimized light-dark cycle and NaNO₃ loading were determined as 11.6/8.4 (h/h) and 15.54 g/L, 12/12 (h/h) and 16.23 g/L, and 12/12 (h/h) and 6.63 g/L, respectively. The multi-response optimization showed that the highest SGR of 0.359 day⁻¹, biomass productivity of 50.663 g/L day⁻¹ and LP of 14.114 mg/L day⁻¹ can be accomplished at culture environments of 12/12 (h/h) light-dark cycles and 10.38 g/L NaNO₃. These results suggest that the central composite design with desirability function-based technique is useful for design and operation of photobioreactors to produce lipid from microalgae. Analysis of variance was employed to explore the significance of the factors affecting microalgal growth as well as biomass and lipid productivities. The predicted optimized culture conditions were experimentally confirmed (error < 6%) indicating the process is robust and reliable.