Advanced Metabolic Engineering Approaches and Renewable Energy to Improve Environmental Benefits of Algal Biofuels: LCA of Large-Scale Biobutanol Production with Cyanobacteria Synechocystis PCC6803

Abstract Microalgae have the potential to serve as sustainable biocatalysts for direct sun-to-bioproduct approaches, e.g. for the synthesis of biofuels. Genetic engineered mutants with a higher photon conversion efficiency of sunlight into biofuels of interest are capable to serve as powerful green cell factories. These advanced metabolic engineering approaches are expected to have environmental benefits, especially for climate protection.The Life Cycle Assessment (LCA) on these novel technologies for the continuous production of algal biobutanol are based on unique and until now unpublished data from a pilot plant. Applying an upscaling approach the environmental impacts of algal biobutanol production at large-scale (20 ha plant) are presented for different scenarios. The results of the prospective LCA show that the higher productivity of the genetically engineered cyanobacteria Synechocystis PCC6803 and its specific feature of discharging the product biobutanol into the medium has a positive impact on the environment. However, electricity demand required for algae cultivation and product harvest overcompensates this advantage. The scenario calculations show that a positive climate gas balance can only be achieved if renewable energy is used.These results indicate the importance of genetic engineering and the energy transition for a fully renewable electricity supply to take full advantage of their environmental potential. Besides, the importance of applying upscaling approaches in LCA for a fairer comparison with mature reference technologies is demonstrated.