A theoretical model for predicting biomass growth in semi-continuous mode under sparging with CO2-enriched air was developed. The model includes gas-to-liquid mass transfer, algal uptake of carbon dioxide, algal growth kinetics, and light and temperature effects. The model was validated using experimental data on growth of two microalgal species in an internally illuminated photobioreactor: Nannochloropsis salina under gas flow rates of 800 and 1200 mL min(-1) and CO2 enrichments of 0.5, 1, and 2%; and Scenedesmus sp. at a gas flow rate of 800 mL min(-1) and CO2 enrichments of 3 and 4%. Temporal algal concentration profiles predicted by the model under semi-continuous mode with harvesting under the different test conditions agreed well with the measured data, with r(2) values ranging from 0.817 to 0.944, p < 0.001. As demonstrated, this model can be beneficial in predicting temporal variations in algal concentration and in scheduling harvesting operations under semi-continuous cultivation mode. (C) 2012 Elsevier Ltd. All rights reserved.