Microalgae biodiesel has attracted considerable attention as a potential substitute for fossil fuels and biodiesel from food crops. Nevertheless, its reported climate impacts in the scientific literature vary significantly. This article describes and synthesizes the range of results found in the life cycle assessment (LCA) literature regarding microalgae biodiesel studies to investigate whether particular parameters, e.g. technologies, were associated with higher or lower greenhouse gas (GHG) emissions so that a best practice can be inferred from currently available LCA data and thereby recommended. A systematic literature review and meta-regression analysis (MRA) of 36 LCA studies that report on the GHG emissions of microalgae biodiesel was conducted. An assessment of key aspects, including modelling choices and technologies, was performed. Furthermore, MRA models were formulated considering several variables of interest describing both technical and modelling choices to identify the main causes for the variability in GHG emissions per MJ of biodiesel. Variables chosen include: microalgae species; culture medium; cultivation system; source of CO2; extraction technology; conversion technology; system boundary; geographical scope; inclusion or exclusion of capital goods; and how multifunctionality was handled. The reviewed studies altogether reported 308 results ranging from −0.7 to 3.8 kg CO2 eq. MJ−1biodiesel, portraying 19 different system configurations. Despite the comprehensive range of variables assessed, the models generated could not plausibly explain that the variability in GHG emissions depends either on the technologies considered or on the methodological choices adopted. However, the following relationships could be observed: location in Europe and high oil productivity were associated with lower emissions, whilst dry extraction should be avoided for leading to higher GHG emissions, on average. There is a large degree of variability within the technologies considered, as well as the methodological choices adopted, so that no robust conclusions could be drawn from the MRA. Notwithstanding, average GHG emissions reported were more than twice as high as fossil diesel and, while there are some studies showing large benefits, none of the various algae technologies performed consistently better than fossil diesel, questioning the climate-mitigation potential of microalgae biodiesel.

中文翻译：

---

微藻生物柴油生命周期温室气体平衡的荟萃分析

微藻生物柴油作为化石燃料和来自粮食作物的生物柴油的潜在替代品引起了相当多的关注。然而，其在科学文献中报告的气候影响差异很大。本文描述并综合了生命周期评估 (LCA) 文献中关于微藻生物柴油研究的结果范围，以调查特定参数（例如技术）是否与更高或更低的温室气体 (GHG) 排放相关，以便最佳实践可以从当前可用的 LCA 数据推断，从而推荐。对 36 项 LCA 研究进行了系统的文献回顾和元回归分析 (MRA)，这些研究报告了微藻生物柴油的温室气体排放。对关键方面进行了评估，包括建模选择和技术。此外，MRA 模型的制定考虑了几个感兴趣的变量，这些变量描述了技术和建模选择，以确定每 MJ 生物柴油 GHG 排放量变化的主要原因。选择的变量包括：微藻物种；培养基；栽培系统；二氧化碳的来源；提取技术；转换技术；系统边界；地理范围；包括或排除资本货物；以及如何处理多功能性。审查的研究共报告了 308 个结果，范围从 -0.7 到 3.8 kg CO2 eq。MJ−1biodiesel，描绘了 19 种不同的系统配置。尽管评估的变量范围很广，但生成的模型无法合理解释温室气体排放的可变性取决于所考虑的技术或所采用的方法选择。但是，可以观察到以下关系：位于欧洲的位置和高石油生产率与较低的排放量相关，而应避免干法提取，因为平均而言会导致较高的温室气体排放量。所考虑的技术以及所采用的方法选择存在很大差异，因此无法从 MRA 中得出可靠的结论。尽管如此，报告的平均温室气体排放量是化石柴油的两倍多，虽然有一些研究显示出巨大的好处，但没有一种藻类技术的表现始终优于化石柴油，这对微藻生物柴油的气候缓解潜力提出了质疑。平均而言，应避免干法提取，因为这会导致更高的温室气体排放。所考虑的技术以及所采用的方法选择存在很大差异，因此无法从 MRA 中得出可靠的结论。尽管如此，报告的平均温室气体排放量是化石柴油的两倍多，虽然有一些研究显示出巨大的好处，但没有一种藻类技术的表现始终优于化石柴油，这对微藻生物柴油的气候缓解潜力提出了质疑。平均而言，应避免干法提取，因为这会导致更高的温室气体排放。所考虑的技术以及所采用的方法选择存在很大差异，因此无法从 MRA 中得出可靠的结论。尽管如此，报告的平均温室气体排放量是化石柴油的两倍多，虽然有一些研究显示出巨大的好处，但没有一种藻类技术的表现始终优于化石柴油，这对微藻生物柴油的气候缓解潜力提出了质疑。