The road to cleaner biofuels: A comparative impact study focused on Australia's decarbonisation journey

This study explores a pathway to decarbonising biofuel production by comparing hybrid renewable configurations, incorporating solar and geothermal energy, with a grid electricity scenario to identify the most environmentally sustainable approach. Five biodiesel production methods— alkaline-catalysed, acid-catalysed, two-step transesterification, electrolysis, and supercritical transesterification—were assessed for producing biodiesel from 1 kg of Chlorella vulgaris oil using the Australian Life Cycle Assessment Society (ALCAS) method, validated through ReCiPe 2016 Midpoint and Endpoint approaches. Among all methods, hybrid supercritical transesterification demonstrated the lowest environmental impact, achieving a global warming potential of 0.49 kg CO 2 eq, marking a 98.4 % reduction compared to grid-powered acid transesterification, the most emission-intensive process. Single score results further confirmed these benefits, showing substantial improvements across human health, ecosystem, and resource impact categories. Uncertainty analysis validated the consistency of these findings, demonstrating that the hybrid energy system outperformed grid electricity across all production methods, emphasising the critical role of renewable energy integration in reducing emissions and environmental burdens. Moreover, full adoption of the hybrid biodiesel system could contribute 6.4 % toward Australia's 2030 climate target, avoiding 2.9 million tons CO 2 eq annually. If implemented from 2025 to 2050, cumulative reductions could reach 72.5 million tons CO 2 eq, significantly supporting Australia's net-zero goals. • Carbon hotspot assessment was performed for microalgae-based biodiesel pathways. • A new geothermal and solar energy setup was assessed for biodiesel production. • Hybrid supercritical transesterification achieved the lowest environmental impacts. • Findings indicate a 2.9 Mt CO 2 eq annual emission reduction potential.