Single-step integrated technology for enhanced CO2 biofixation and efficient lipid extraction in microalgal system including a water-immiscible solvent

Abstract

The potential of microalgae for both carbon fixation and energy sustainability has been demonstrated. However, the low CO2 biofixation rate and high cost of lipid extraction restrict its large-scale development. This paper proposes a novel integrated technology for enhanced CO2 biofixation and efficient lipid extraction in microalgal system by adding water-immiscible solvent N-heptane over the culture medium. N-heptane can act as a ‘carbon sink’ and ‘extract agent’ without causing significant damage to microalgal cells. Specifically, N-heptane with the volume percentages of 4, 8, 12, 25 and 42 % was added to Chlorella sp. culture systems. Simulated flue gas containing 15 vol% CO2 in nitrogen gas was used as the sole carbon source. The maximum biomass concentration (0.84 g·L-1) and specific growth rate (0.23 d-1) were achieved with 12 % N-heptane. These values were higher than blank culture by 12.3 % (biomass concentration) and 56.9 % (specific growth rate). The CO2 biofixation rate increased with N-heptane to a maximum value of 220.2 mg·L-1·d-1, which was 64.7 % higher than that of the blank culture. Meanwhile, the system has a potential for the generation of biofuels with a maximum lipid amount of 2.82 g·gAlgae-1 in this single step approach.