Enhancement of CO2 tolerance of Chlorella vulgaris by gradual increase of CO2 concentration

Summary Chlorella vulgaris UTEX259 was cultivated using two different methods of gas supply. In one method the CO₂ concentration in bubbled gas was held constant and in the other method it was increased gradually. Algal growth was almost linear after a short period of lag phase in both methods. With the constant CO₂ concentration, the CO₂ fixation rate in the linear growth phase decreased over 10%(v/v) CO₂, while the rate increased up to 6% CO₂. However, the rate was enhanced by using the latter incremental increase method, especially under a higher concentration of CO₂. The maximum rate of CO₂ fixation was 52 mg CO₂/l·h at 20% CO₂ during the gradual increase of CO₂ concentration.