Growth and Nutrient Utilization of Green Algae in Batch and Semicontinuous Autotrophic Cultivation Under High CO₂...

The growth performance of Chlorella protothecoides, Chlorella pyrenoidosa, and Chlorella sp. in autotrophic cultivation with 10% carbon dioxide (CO₂) 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% CO₂ 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 CO₂ flow rate and inoculation ratio in batch cultivation, light intensity considerably improved biomass yield, N and P assimilation, and CO₂ 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% CO₂, 2:1 provided the highest biomass productivity (0.19 g/L/day) and CO₂ 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% CO₂. Compared with the batch cultivation of C. protothecoides, semicontinuous cultivation improved the CO₂ fixation rate (by 1.5-2 times) and CO₂ utilization efficiency (by 3-6 times) of C. protothecoides.