Potential microalgal strains for converting flue gas CO2 into biomass

A screening method using 15% CO2 (v/v) as screening stress and a spotting plate method was developed to isolate microalgae with the potential to convert flue gas CO2 to biomass. A total of six microalgal strains, belonging to the genera Chlorella, Heynigia, Desmodesmus, and Scenedesmus, were isolated from ponds near metallurgical/cement/power plants. The growth of these isolated strains was dramatically promoted at 5 to 15% CO2 when they were cultivated in bubble column photobioreactors aerating with 0.03%, 5%, 10%, and 15% CO2. The growth of Heynigia riparia SX01 in particular showed substantial improvement with the increase of CO2 concentrations from 5 to 15%. Furthermore, the maximum biomass, overall biomass productivity, maximum biomass productivity, and maximum CO2 fixation rate of these microalgal strains greatly increased at 5 to 15% CO2 as well. Chlorella sorokiniana GS03 showed the highest values in maximum biomass productivity (0.36 g L−1 day−1) and maximum CO2 fixation rate (0.66 g L−1 day−1) at 5% CO2. Heynigia riparia SX01 exhibited the highest values of maximum biomass (3.28 g L−1), overall biomass productivity (0.27 g L−1 day−1), maximum biomass productivity (0.39 g L−1 day−1), and maximum CO2 fixation rate (0.71 g L−1 day−1) at 15% CO2. This study provides not only an efficient screening method obtaining microalgae with wide CO2 tolerance but also microalgal strains utilizing high levels of CO2 up to 15% to produce biomass, which contributes to further exploration in converting real flue gas CO2 into biomass feedstock.