Evaluating microalgal integrated biorefinery schemes: Empirical controlled growth studies and life cycle assessment

Two freshwater and two marine microalgae species were grown under nitrogen replete and deplete conditions evaluating the impact on total biomass yield and biomolecular fractions (i.e. starch, protein, and lipid). A life cycle assessment was performed to evaluate varying species/growth conditions considering each biomass fraction and final product substitution based on energy consumption, greenhouse gas emissions (GHG), and eutrophication potential. Lipid for biodiesel was assumed as the primary product. Protein and carbohydrate fractions were processed as co-products. Composition of the non-lipid fraction presented significant trade-offs among biogas production, animal feed substitution, nutrient recycling, and carbon sequestration. Maximizing total lipid productivity rather than lipid content yielded the least GHG emissions. A marine, N-deplete case with relatively low lipid productivity but effective nutrient recycling had the lowest eutrophication impacts. Tailoring algal species/growth conditions to optimize the mix of biomolecular fractions matched to desired products and co-products can enable a sustainable integrated microalgal biorefinery.