Some characteristics of microalgae isolated in Taiwan for biofixation of carbon dioxide

To contribute the biological mean of CO2 fixation, more than 200 microalgal isolates were screened from lakes, ponds, sediments, hog wastewater, paddy fields, hot springs, and seawater in Taiwan. Two unicellular microalgae, Chlorella sp. NTU-H15 and Chlorella sp. NTU-H25, were isolated from hog wastewater. In the laboratory, they were able to grow up even in aeration containing CO2 up to 40% and have growth rates of 0.21 to 0.22 g dry wt l-1 d-1 at 20% CO2. Both algae had the same growth rate in the range from 5 to 40% CO2 and had a similar light response between 190 and 589 μmol m-2 s-1. Chlorella sp. NTU-H15 had a higher growth rate than Chlorella sp. NTU-H25 at pH 4.0 and ≥35°C. Chlorella sp. NTU-H15 was able to tolerate high concentrations of CO2, high cell density, and a broad-range of temperature and pH. Each liter of Chlorella sp. NTU-H15 produced 1.8 g of dry cell. The maximum growth rate was 0.28 g dry wt l-1 d-1, and the specific growth rate was 0.27 d-1 at 15% CO2. Each mg of chlorophyll produced 1.6 mM O2 min -1 at 700 μmol m-2 s-1 at 30°C and 10 mM NaHCO3. While each liter of Chlorella sp. NTU-H25 produced 1.7 g of dry cell, the maximum growth rate was 0.27 g dry wt l-1 d-1, and the specific growth rate was 0.27 d-1. Both isolates are suitable for dense cultivation to fix CO2 directly and to produce cell biomass.