Sustainable valorization of flue gas CO2 and wastewater for the production of microalgal biomass as a biofuel feedstock in closed and open reactor systems

Abstract

As a green process development initiative, the potential of valorization of wastes, like domestic wastewater and coal-fired flue gas CO₂, by Scenedesmus sp. was examined in closed and open reactor systems. The green microalga, when cultivated in the photobioreactor, produced 35.6% lipid and 10.4% carbohydrate with 46.1% increase in biomass productivity (185.7 ± 7.3 mg L⁻¹ d⁻¹) at an optimal flue gas CO₂ concentration of 2.5% as compared to the control (0.03%, CO₂). The culture also showed significant remediation of ammonium, nitrate, phosphate and COD by about 95%, 66%, 72%, and 93%, respectively. The raceway pond culture supplemented with 2.5% flue gas CO₂ produced 24.1% lipid and 19.2% carbohydrate with 36% rise in biomass productivity (97.1 ± 2.7 mg L⁻¹ d⁻¹) when compared to the control. Fatty acid profiling showed a higher percentage of C₁₆/C₁₈. Thus, this study realized the goal and implemented the mandate of developing green and sustainable processes for converting inexpensive, but polluting wastes like flue gas and wastewater, into biofuel feedstock through microalgal cultivation.