Carbon dioxide mitigation and biodiesel production by a marine microalga under mixotrophic mode by using transesterification by-product crude glycerol: A synergy of biofuels and waste valorization

Abstract

The present work integrates carbon sequestration and waste reclamation with biofuel production into a single dynamic for encouraging eco-friendlier approaches ensuring environmental sustainability. To achieve improved carbon capturing and lipid production, a marine microalga Picochlorum soloecismus was selected. The maximum productivities of biomass and lipid were asserted to be 0.24 ± 0.02 gL−1d−1 and 58.2 ± 0.2 mgL−1d−1 under a CO2 supply of 17.0% at 0.7 vvm aeration in a 5 L photobioreactor under photoautotrophic condition. A low-priced mixotrophic medium was designed using CO2 with the transesterification by-product, i.e., crude glycerol. This produced maximum biomass and lipid productivities of 0.67 ± 0.04 and 0.13 ± 0.01 gL−1d−1 at a carbon fixation rate of 0.77 ± 0.06 gL−1d−1. The effect of mixotrophy was also investigated on a modified culture medium, i.e. Optimized ASN (Artificial Seawater Nutrient) prepared in our recent study generating a maximum lipid productivity of 0.31 ± 0.02 gL−1d−1at a carbon fixation rate of 0.80 ± 0.07 gL−1d−1. The use of crude glycerol in place of commercial glycerol for mixotrophy can reduce the medium cost by 22-fold. The methyl ester profile of biodiesel obtained under mixotrophy exhibited higher proportion of saturated fats and lower fraction of unsaturated fats. The fuel parameters lied within the established biodiesel standards.