Multiobjective optimization of microalgae (Chlorella sp.) growth in a photobioreactor using Box-Behnken design approach

A parameter optimization approach to maximize the specific growth rate of the Chlorella vulgaris microalgae species, its biomass productivity, and CO₂ capture rate was investigated. The Box-Behnken experimental design technique was applied with temperature, nitrogen to phosphorus ratio, and light-dark cycle per day, as the growth controlling parameters. For each response, a quadratic model was developed separately describing the algal specific growth rate, biomass productivity, and CO₂ capture rate, respectively. The maximum specific growth rate of 0.84/d was achieved at 25°C, with a nitrogen to phosphorus ratio of 3.4:1, and light-dark cycles of 24/0 h. Maximum biomass productivity of 147.3 mg/L-d was noted at 30°C, with a nitrogen to phosphorus ratio of 3:1, and light-dark cycles of 12/12 h. Also, the maximum CO₂ capture rate of 159.5 mg/L-d was also obtained at 30°C, with a nitrogen to phosphorus ratio of 4:1, and light-dark cycles of 23/1 h. A multi-response optimization method was applied to maximize the specific growth rate, biomass productivity, and CO₂ capture rate, simultaneously. The optimal set of 30°C, a nitrogen to phosphorus ratio 3:1, and light-dark cycles 16/8 h, provided the maximum specific growth rate of 0.66/day, biomass productivity of 147.6 mg/L-d, and CO₂ capture rate of 141.7 mg/L-d.