Quantitative analysis of spirulina platensis growth with CO2 mixed aeration

Abstract

The growth characteristics of Spirulina platensis were investigated using four photo-bioreactors with CO2-mixed air flows. Each reactor was operated under a specific condition: 3% CO2 at 50 mL/min, 3% CO2 at 150 mL/min, 6% CO2 at 50 mL/min, and 6% CO2 at 150 mL/min. The 3% CO2 at 150 mL/min condition produced the highest algal growth rate, while the 6% CO2 at 150 mL/min conditioned produced the lowest. The algal growth performance was suitably assessed by the linear growth curve rather than the exponential growth. The medium pH decreased from 9.5 to 8.7-8.8 (3% CO2) and 8.4-8.5 (6% CO2), of which trends were predicted only by the pH-carbonate equilibrium and the reaction kinetics between dissolved CO2 and HCO3-. Based on the stoichiometry between the nutrient amounts and cell elements, it was predicted that depleted nitrogen (N) at the early stage of the cultivation would reduce the algal growth rates due to nutrient starvation. In this study, use of the photobioreactors capable of good light energy distribution, proper ranges of CO2 in bubbles and medium pH facilitated production of high amounts of algal biomass despite N limitation.