Improved biomass and lipid production in a mixotrophic culture of Chlorella sp. KR-1 with addition of coal-fired flue-gas

• CO2-rich coal-fired flue gas could be effectively used for mixotrophic algal growth.
• Fed-batch system with air supply in dark resulted in the highest lipid productivity.
• Bacterial community of KR-1 depended markedly on organic feeding(s) and aeration.
• Fatty acid composition of KR-1 meets the key biodiesel standards.

Industrial CO2-rich flue-gases, owing to their eco-toxicity, have yet to be practically exploited for microalgal biomass and lipid production. In this study, various autotrophic and mixotrophic culture modes for an oleaginous microalga, Chlorella sp. KR-1 were compared for the use in actual coal-fired flue-gas. Among the mixotrophic conditions tested, the fed-batch feedings of glucose and the supply of air in dark cycles showed the highest biomass (561 mg/L d) and fatty-acid methyl-ester (168 mg/L d) productivities. This growth condition also resulted in the maximal population of microalgae and the minimal population and types of KR-1-associated-bacterial species as confirmed by particle-volume-distribution and denaturing-gradient-gel-electrophoresis (DGGE) analyses. Furthermore, microalgal lipid produced was assessed, based on its fatty acid profile, to meet key biodiesel standards such as saponification, iodine, and cetane numbers.