Effect of inorganic carbon on photoautotrophic growth of microalga <i>Chlorococcum littorale</i>

Abstract

The growth rate of a highly CO(2)-tolerant green alga, Chlorococcum littorale, was investigated in semi-batch cultures at a temperature of 22 degrees C, a light intensity of 170 micromol-photon m(-2) s(-1) and CO(2) concentrations ranging from 1 to 50% (v/v) at atmospheric pressure. In the experiments, solutions were bubbled with CO(2) and N(2) gas mixtures to adjust CO(2) concentrations to minimize the influence of O(2). Growth rate, which was defined in terms of a specific growth rate mu, decreased with increasing CO(2) concentration at the conditions studied. The inhibition of growth by CO(2) gas could be attributed to the concentration of inorganic carbon in the culture medium. A growth model is proposed where key assumptions are the formation of bicarbonate ion HCO(3) (-) as substrate for algal growth and equilibrium between CO(2) inhibitor. The proposed growth model based on the Monod equation agreed with the experimental data to within 5% and provides better correlation than the conventional inhibition model, especially in the high CO(2) concentration region.