Growth and Nutrient Utilization of Green Algae in Batch and Semicontinuous Autotrophic Cultivation Under High CO Concentration.

The growth performance of Chlorella protothecoides, Chlorella pyrenoidosa, and Chlorella sp. in autotrophic cultivation with 10% carbon dioxide (CO) was evaluated. The biomass production of C. protothecoides, along with its carbon, nitrogen (N), and phosphorus (P) utilization, in batch and semicontinuous autotrophic cultivation with 20% CO was also determined. Among the three algae species, C. protothecoides obtained the highest biomass yield (1.08 g/L) and P assimilation (99.4%). Compared with the CO flow rate and inoculation ratio in batch cultivation, light intensity considerably improved biomass yield, N and P assimilation, and CO utilization. In the semicontinuous cultivation of C. protothecoides, a hydraulic retention time (HRT) of 8 days kept the system at a stable running state, thereby demonstrating that an HRT of 8 days was better than an HRT of 5 days. Among the three N/P ratios for C. protothecoides in semicontinuous cultivation with 20% CO, 2:1 provided the highest biomass productivity (0.19 g/L/day) and CO fixation rate (0.37 g/L/day). Therefore, this lower N/P ratio is more suitable than 10:1 and 50:1 for the growth of C. protothecoides with 20% CO. Compared with the batch cultivation of C. protothecoides, semicontinuous cultivation improved the CO fixation rate (by 1.5-2 times) and CO utilization efficiency (by 3-6 times) of C. protothecoides.