Optimization of CO₂ Biofixation by Chlorella vulgaris Using a Tubular Photobioreactor

The effects of various CO₂ concentrations in CO₂ bioconversion by cultivation of microalga Chlorella vulgaris were investigated using a vertical tubular photobioreactor. The response surface technique with central composite design was applied to model the CO₂ biofixation rate, the specific growth rate (SGR), and the biomass productivity of C. vulgaris as function of CO₂ concentration and cultivation time. The developed nonlinear model was employed to determine the optimum CO₂ concentration in an air-CO₂ mixture and the cultivation time for maximum CO₂ biofixation, SGR, and microalgae biomass productivity. In addition, a multiple responses optimization method was also applied to determine the maximum CO₂ uptake rate, the SGR, and the biomass productivity, simultaneously. The predicted optimum values agreed well with the experimental data.