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

Abstract

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/MJBuOH and the CED from 3.8 to 13 MJ/MJBuOH. 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.

The “Zero Miles Product” Concept Applied to Biofuel Production: A Case Study

“…Thus, both the environmental benefits as well as the gas emission during the whole process are evaluated. As reported by several of these studies [14][15][16], one of the main drawbacks in the biorefinery approach is the feedstock's selection and collection: some feedstocks are produced in a particular area, but they are available in low amounts throughout the year [17], while others are available in high amounts, but their production requires broad land use, increasing the collection/transport costs [18]. In order to overcome this problem, some studies proposed the "multi-feedstock" biorefinery concept: a biorefinery able to pretreat and convert different types of feedstocks into fermentable sugars [19].…”

“…Nowadays, biofuel production through biotechnological processes has been entirely analyzed with the so-called "cradle-to-grave" approach [14]. This analysis allows to identify the main issues of a given process by considering the whole production chain: from the starting feedstock to the final product use/disposal.…”

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

“…The comparison with other studies addressing this technology, e.g. Nilsson et al [64], is challenging because these are theoretical studies based only on literature assumptions to construct a hypothetical production scheme with different reactors and conditions. Nevertheless, it can be noted that one of the productivities used by Nilsson et al [64] is in the same range of the biobutanol productivity presented in this work (600 mg/L/day), but significantly higher in comparison with previous literature.…”

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

“…This study is the rst LCA of biobutanol production through genetically modi ed algae carried out with real data. There are currently other works that address this issue [46], however, these assessments are based on assumptions from the literature to construct a hypothetical production scheme. The fact that these are purely theoretical studies, highlights the importance of the present work.…”