Environmental impacts and limitations of third‐generation biobutanol: Life cycle assessment of n‐butanol produced by genetically engineered cyanobacteria

• Published in: Journal of Industrial Ecology
• Main Authors: Nilsson, Astrid, Shabestary, Kiyan, Brandão, Miguel, Hudson, Elton P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Northern Sweden
• Online Access: http://dx.doi.org/10.1111/jiec.12843; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jiec.12843; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jiec.12843

Abstract Photosynthetic cyanobacteria have attracted interest as production organisms for third‐generation biofuels, where sunlight and CO 2 are used by microbes directly to synthesize fuel molecules. A particularly suitable biofuel is n ‐butanol, and there have been several laboratory reports of genetically engineered photosynthetic cyanobacteria capable of synthesizing and secreting n ‐butanol. This work evaluates the environmental impacts and cumulative energy demand (CED) of cyanobacteria‐produced n ‐butanol through a cradle‐to‐grave consequential life cycle assessment (LCA). A hypothetical production plant in northern Sweden (area 1 ha, producing 5–85 m 3 n ‐butanol per year) was considered, and a range of cultivation formats and cellular productivity scenarios assessed. Depending on the scenario, greenhouse gas emissions (GHGe) ranged from 16.9 to 58.6 gCO 2 eq/MJ BuOH and the CED from 3.8 to 13 MJ/MJ BuOH . Only with the assumption of a nearby paper mill to supply waste sources for heat and CO 2 was the sustainability requirement of at least 60% GHGe savings compared to fossil fuels reached, though placement in northern Sweden reduced energy needed for reactor cooling. A high CED in all scenarios shows that significant metabolic engineering is necessary, such as a carbon partitioning of >90% to n ‐butanol, as well as improved light utilization, to begin to displace fossil fuels or even first‐ and second‐generation bioethanol.