Literature repots on the CO2 effect are greatly contradictory. Some of them showed that the
concentration of CO2 aeration above 5% could be harmful to microalgae cells and inhibit the microalgae growth (Chiu et al. 2008). Tang et al. (2011) reported that Scenedesmus obliquus and Chlorella pyrenoidosa could grow well under CO2 concentrations ranging from 5% to 30%. They even could grow at the CO2 level of 50%. Ota et al. (2009) reported the maximum biomass concentration of highly CO2 tolerant C. littorale was about 0.5 g/l at the CO2 concentration of 50% after 14 days cultivation.