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

Abstract

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.