Used-cooking-oil biodiesel: Life cycle assessment and comparison with first- and third-generation biofuel

The environmental sustainability of second-generation biodiesel (used-cooking-oil) was examined, at industrial-scale, in Greece. The total carbon and environmental footprint per tonne of biodiesel production was similar to 0.55t CO2 eq (i.e. similar to 14g CO2 eq/MJ) and 58.37 Pt, respectively. This is similar to 40% lower compared to first-generation biodiesel, an order of magnitude lower than the third-generation (microalgae), since the latter is not a fully-fledged technology yet. A threefold reduction in environmental impacts was observed compared to petrodiesel. Environmental hotspots include energy inputs to drive the process, followed by methanol (CH3OH) and potassium methoxide (CH3KO) consumption. Glycerol (C3H8O3) and potassium sulfate (K2SO4), both process co-products, resulted to avoided environmental burdens. Furthermore, used-cooking-oil valorisation for biodiesel production can address water pollution concerns from its disposal to the sewage system. The total distance and means of transport were found to influence the system's environmental sustainability. Strong incentives for used-cooking-oil recycling, widespread collection systems, and biodiesel supply chain optimization are still pending in Greece, Europe, and further afield. Given its overall low environmental footprint and capability to be produced at commercial scales, the second-generation biodiesel, which currently represents 15% of the biodiesel market in Greece, could act as a stepping-stone in decarbonizing Europe's transport sector and improving supply and energy security. (C) 2020 Elsevier Ltd. All rights reserved.