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

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. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).