High photosynthetic productivity of green microalga Chlorella sorokiniana

The batch culture of a newly isolated strain of a green microalga, Chlorella sorokiniana, was carried out using a conical helical tubular photobioreactor. The isolate was capable of good growth at 40°C under an airstream enriched with 10% CO2. The maximum photosynthetic productivity was 34.4g of dry biomass/(m2 of installation area · d) (12-h light/12-h dark cycle) when the cells were illuminated with an average photosynthetic photon flux density (photosynthetically active radiation ([PAR] 400–700 nm) simulating the outdoors in central Japan (0.980 mmol photons/[m2·s]). This corresponded to a photosynthetic efficiency of 8.67% (PAR), which was defined as the percentage of the light energy recovered as biomass (394 kJ/[reactor·d]) to the total light energy received (4545 kJ/[reactor·d]). A similarly high photosynthetic efficiency (8.12% [PAR]) was also attained in the combined presence of 10% CO2, 100 ppm of NO, and 25 ppm of SO2. Moreover, good photosynthetic productivity was also obtained under high temperature and high light intensity conditions (maximum temperature, 46.5°C; 1.737 mmol photons/[m2·s]), when simulating the strong irradiance of the midday summer sun. This strain thus appears well suited for practical application for converting CO2 present in the stack gases emitted by thermal power plants and should be feasible even during the hot summer weather.