Ability of an alkali-tolerant mutant strain of the microalga Chlorella sp. AT1 to capture carbon dioxide for increasing carbon dioxide utilization efficiency

An alkali-tolerant Chlorella sp. AT1 mutant strain was screened by NTG mutagenesis. The strain grew well in pH 6–11 media, and the optimal pH for growth was 10. The CO₂ utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO₂ aeration for 10, 20 and 30 min at 3-h intervals were approximately 80, 42 and 30%, respectively. In alkaline medium (pH = 11) with intermittent 10% CO₂ aeration for 30 min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.710 g L⁻¹ d⁻¹, respectively. When Chlorella sp. AT1 was aerated with 10% CO₂ intermittently for 30 min at 3-h intervals in semi-continuous cultivation for 21 days, the biomass concentration and biomass productivity were 4.35 g L⁻¹ and 0.726 g L⁻¹ d⁻¹, respectively. Our results show that CO₂ utilization efficiency can be markedly increased by intermittent CO₂ aeration and alkaline media as a CO₂-capturing strategy for alkali-tolerant microalga cultivation.