Photobioreactor strategies for improving the CO 2 fixation efficiency of indigenous Scenedesmus obliquus CNW-N: Statistical optimization of CO 2 feeding, illumination, and operation mode

Abstract

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.