CO2 capturing by chlorella vulgaris in a bubble column photo-bioreactor; Effect of bubble size on CO2 removal and growth rate

In this study, a modified gas feeding bubble column photo-bioreactor was utilized for microalgae cultivation and CO2 capturing. By applying response surface methodology, the optimum values of temperature, pH, light intensity, aeration rate, light-dark cycle and time were determined as 25 degrees C, 8, 2700 lx, 0.5 LPM and 16-8 h, respectively. Two air spargers (with different aperture size) were used to study the effect of the bubble size on the CO2 removal and microalgae growth rate. Besides, the inlet air was humidified to avoid the evaporation from the photo-bioreactor. For the smaller bubbles and 7% CO2 concentration, the maximum values for the CO2 fixation rate, productivity and concentration of microalgae were determined to be 633.73 mg L(-1)d(-1), 337 mg L(-1)d(-1) and 4244 mg L-1, respectively. CO2 utilization efficiency was 35% for the smaller bubbles, showing a 15% increase over that for the larger bubbles.