The use of fossil fuels in the transportation sector has significantly increased the greenhouse gas (GHG) emissions, leading to concerns about their environmental impact. As a result, biofuels have been promoted as a promising alternative to fossil fuels to mitigate GHG emissions. However, while biofuels are considered a low-carbon solution, there are concerns that its widespread use could have unforeseen environmental effects. This study analyzes the intricacies involved in biofuel’s life cycle assessment (LCA). Fifty-three peer-reviewed studies were examined, covering a broad range of biofuels produced from over 25 different feedstocks. The literature review focused mainly on research published from 2012 to 2022 to avoid outdated information. The study found that second-generation biofuels have a greater potential for reducing GHG emissions than first-generation biofuels. However, the GHG emissions from third-generation biofuels are higher than those from conventional fuel, ranging from 10.2 to 1910 g CO2 eq. / MJ. The net energy ratio for biofuels ranges from 1.23 to 12.49 for first-generation, 0.003 to 15.04 for second-generation, and 3 to 18.5 for third-generation biofuels. The analysis also shows that the water footprint of biofuels is 50–240 times greater than fossil fuels. The study also examines the critical methodological aspects and sources of uncertainty in the LCA of biofuels and suggests solutions to address these problems. Overall, the study highlights the importance of taking a comprehensive approach when assessing the environmental impact of biofuels and the need for continued research to develop sustainable and effective biofuels.
The study shows that second-generation biofuels have a greater potential for reducing GHG emissions than first-generation biofuels. However, the GHG emission from third-generation biofuels exceeds emissions from conventional fuel due to the high electricity consumption in biofuel production. The novelty of the work lies in the critical review of LCA studies and in exploring the critical methodological features and sources of uncertainty in biofuel LCA. This study also contributes to the sustainable development goals by evaluating the GHG emissions and net energy ratio of biofuel production.
The estimated GHG emission of first-generation bioethanol ranges from 0.006 to 167 g CO2 eq. / MJ, and that for biodiesel varies from -7.3 to 329 g CO2 eq. When the average values are taken into account, the GWP of most of the first-generation biofuels is less than those of conventional gasoline (72.8 to 96 g CO2 eq. / MJ). The GHG emissions of second-generation biofuels vary from -15.4 to 178.7 g CO2 eq. / MJ for bioethanol and – 0.21 to 113.8 g CO2 eq. / MJ for biodiesel