Transforming CO2 into Valuable Biomass: Insights from a Thai Chlorella sp.

Rising atmospheric CO2 levels and global temperatures have intensified the need for efficient biological carbon capture systems. Microalgae, particularly Chlorella spp., are promising candidates owing to their ability to utilize CO2 and convert it into biochemically rich biomass under diverse environmental conditions. This study evaluated the performance of a strain of Chlorella sp. isolated from Thailand in CO2 assimilation and biomass production at different temperatures (35 and 42 °C) and varying CO2 concentrations, ranging from 0.04% (air) to 20%. At 35 °C, the strain effectively used up to 10% CO2, yielding a maximum biomass productivity of 0.419 g L-1 d-1 and a CO2 fixation rate of 0.775 g L-1 d-1. The biomass consisted of 51.73% protein and 26.88% carbohydrate on a dry weight basis. Productivity of protein and carbohydrates increased by 4.52- and 4.74-fold, respectively, compared with those of air-aerated cultures. When the temperature was raised to 42 °C, CO2 utilization efficiency decreased. The highest biomass productivity (0.308 g L-1 d-1) and CO2 fixation rate (0.571 g L-1 d-1) were observed at 5% CO2. Under this condition, the biomass maintained a high protein content of 54.82%, corresponding to a 5.3-fold increase in productivity over air-aerated cultures. These results demonstrated that Chlorella sp. exhibits strong tolerance to moderately high temperatures and CO2 concentrations, highlighting its potent