Photobioreactor strategies for improving the CO2 fixation efficiency of indigenous Scenedesmus obliquus CNW-N: statistical optimization of CO2 feeding, illumination, and operation mode.

Statistical experimental design and bioreactor strategies were applied to enhance CO(2) fixation ability of microalga Scenedesmus obliquus CNW-N. Four operating parameters strongly influencing microalgal CO(2) fixation efficiency (namely, CO(2) concentration, CO(2) flow rate, magnesium concentration, and light intensity) were optimized with response surface methodology. The optimal range of parameters achieving the best overall performance of specific growth rate and CO(2) fixation rate was determined with overlay counter plot techniques. Optimal ranges of CO(2) concentration, CO(2) flow rate, magnesium concentration and light intensity were 2.0-2.5%, 0.3-0.5 vvm, 1.7-2.7 mM and 180-250 μmol m(-2) s(-1), respectively, achieving a specific growth rate of >1.22 d(-1) and CO(2) fixation rate of >800 mg L(-1) d(-1). Semi-batch operations further enhanced the biomass productivity, photosynthesis efficiency, and CO(2) fixation rate to 1030 mg L(-1) d(-1), 10.5%, and 1782 mg L(-1) d(-1), respectively. This performance is better than the results reported by most related studies.