A meta-analysis of the life cycle greenhouse gas balances of microalgae biodiesel

Abstract

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.Methods: 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. Results and discussion:The reviewed studies altogether reported 308 results ranging from -0.7 to 3.8 kg CO2 eq MJ -1 biodiesel, 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 are associated with lower emissions, whilst dry extraction should be avoided for leading to higher GHG emissions, on average. Conclusions: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.

An Overview of Algae for Biodiesel Production Using Bibliometric Indicators

“…Examining the life cycle and energy balance of the production of microalgae biomass on a large scale is necessary to analyse the environmental effects of algae-derived biodiesel technology and the profitability of such undertakings [199][200][201]. The life cycle assessment (LCA) of biodiesel made from algae utilising closed and open system cultivations has been the subject of several studies [202][203][204] with Garcia et al [205] conducting a meta-analysis of the life cycle greenhouse gas balances of microalgae biodiesel. Studies on LCA have shown that there is a lot of variation in the technologies taken into account as well as the methodological decisions made, making it impossible to draw reliable conclusions.…”

“…This may indicate inconsistent findings on biodiesel's effectiveness in comparison to a rival fuel (petroleum diesel) [199]. In some studies, for example, the average GHG emissions reported were more than twice as high as fossil diesel, while some studies showed large benefits [205]. Although several researchers have proposed a framework for the environmental effects of producing algae biodiesel, there is still a great deal of variation in the LCA results due to differences in the life-cycle assessment (LCA) assumptions, life-cycle impact assessment (LCIA) included items, and system boundaries (considered in the LCA) [199].…”

Limits to Paris compatibility of CO2 capture and utilization

“…Microalgae biofuel studies were excluded based on the agreement in the most recent reviews, meta-analyses, and harmonized LCA studies that emissions were not reduced consistently compared with fossil fuels [160][161][162] or, on average, even doubled. 163 For each individual combination of CCU technology and type of CO 2 source (fossil, biogenic, or atmospheric), the most recent study with the most complete life cycle inventory was selected. This resulted in 30 studies (1 on direct use, 15 on fuels and chemicals, 8 on mineral carbonates and construction materials, and 6 on EHR), together covering 44 unique CCU technologies and resulting in 74 combinations based on multiple CO 2 sources.…”

Perspective Design of Algae Photobioreactor for Greenhouses—A Comparative Study

“…In the pharmaceutical and food industries, a high added value of products entering the market can be often predicted, which opens a wide range of possibilities for microalgae production applications. Lipid production is currently investigated mainly regarding biofuels production, which is, however, still not competitive enough compared to the existing technologies [9,10], even though the algae biodiesel is of comparable quality with other biodiesels [11]. Intensive research on microalgae cultivation, system optimization, and other aspects of the supply chain is currently being carried out using the most advanced algorithms [12].…”