Photosynthetic cyanobacteria have attracted interest as production organisms for third‐generation biofuels, where sunlight and CO₂ 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 m³ 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 gCO₂eq/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 CO₂ 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.

中文翻译：

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第三代生物丁醇的环境影响和局限性：基因工程蓝细菌生产的正丁醇的生命周期评估

作为第三代生物燃料的生产有机体，光合作用的蓝细菌引起了人们的兴趣，其中微生物直接利用阳光和CO ₂来合成燃料分子。一种特别合适的生物燃料是正丁醇，并且有一些实验室报告表明，能够合成和分泌正丁醇的基因工程光合作用蓝细菌。这项工作通过从摇篮到坟墓的相应生命周期评估（LCA）评估了蓝藻生产的正丁醇的环境影响和累积能量需求（CED ）。瑞典北部的一个假设生产工厂（面积1公顷，生产5-85 m ³ n-每年使用-丁醇），并评估了各种培养方式和细胞生产力方案。根据具体情况，温室气体排放量（GHGe）在16.9至58.6 gCO ₂ eq / MJ _BuOH之间，而CED在3.8至13 MJ / MJ _BuOH之间。仅假设附近有一家造纸厂为热和CO ₂提供废料，与矿物燃料相比，可持续性要求至少要节省60％GHGe，尽管在瑞典北部的工厂减少了反应堆冷却所需的能源。在所有情况下，高CED均表明必须进行大量的代谢工程，例如碳分配> 90％至n丁醇，以及提高的光利用率，开始取代化石燃料，甚至取代第一代和第二代生物乙醇。