Biological fixation of CO₂ by Chlorella sp. HA-1 in a semi-continuous and series reactor system

Characteristics of biological CO₂ fixation by Chlorella sp. HA-1 were investigated in a semi-continuous and series reactor system using an internally illuminated photobioreactor to overcome shortcomings of physicochemical technologies such as adsorption and membrane separation. High CO₂ fixation rate was achieved in the semi-continuous reactor system, in which the dilution ratios of the culture medium were controlled. The average CO₂ fixation rate was maintained almost constantly when the dilution ratio increased by 0.1 increment from the initial value of 0.5. The total removal efficiency of CO₂ was enhanced by employing a series reactor system. The average CO₂ fixation rate increased until 4.013 g CO₂ day^-1 in a series operation of four reactors, compared to 0.986 g CO₂ day^-1 in a batch operation mode. The total CO₂ fixation rate was proportional to the number of reactors used in the series reactor system. In the series reactor system of semi-continuous operation, a large amount of CO₂ was removed continuously for 30 days. These results showed that the present reactor systems are efficient and economically feasible for a biological CO₂ fixation.