Process integration for microalgal lutein and biodiesel production with concomitant flue gas CO2 sequestration: a biorefinery model for healthcare, energy and environment

In this study, a green microalgal feedstock based biorefinery was developed by process optimization and integration with a view to sequestering flue gas CO2 and synthesizing lutein and lipid for environmental, healthcare and biofuel applications, respectively. Out of the four microalgal cultures tested in a 2 L airlift photobioreactor, Chlorella minutissima showed comparatively higher productivities of both lutein (2.37 +/- 0.08 mg L-1 d(-1)) and lipid (84.3 +/- 4.1 mg L-1 d(-1)). Upon optimization of the critical process parameters using artificial neural network modeling and the particle swarm optimization (ANN-PSO) technique, the productivities of lutein and lipid were enhanced to 4.32 +/- 0.11 mg L-1 d(-1) and 142.2 +/- 5.6 mg L-1 d(-1) respectively, using pure CO2 sequestered at a rate of 1.2 +/- 0.03 g L-1 d(-1). One of the most interesting findings was that the lutein and lipid productivities were not significantly affected by the use of toxic flue-gas, when diluted to 3.5% CO2 with air, under the same process conditions, suggesting the possible commercial usefulness of flue-gas carbon. Another major achievement is that a single step ethanol-hexane based extraction procedure, followed by parallel saponification and trans-esterification, resulted in the simultaneous recovery of 94.3% lutein and 92.4% fatty acid methyl ester. Therefore, the potential industrial significance of this study lies in the development of an integrated biorefinery that may prove to be a sustainable technology platform towards addressing some contemporary challenges in healthcare, energy and environment through concomitant production of microalgal lutein as a nutraceutical and biodiesel as an alternative fuel, coupled with flue gas CO2 sequestration.