Integrating life cycle assessment and environmental life cycle costing to evaluate used cooking oil valorisation routes.

Used cooking oil (UCO) is an abundant feedstock to produce renewable energy and bio-based materials. However, valorisation routes differ substantially in environmental performance and economic viability. This study identifies the UCO valorisation route offering the best overall performance when both dimensions are assessed simultaneously, supporting more sustainable waste management strategies. An integrated environmental and techno-economic assessment was conducted for five routes: biodiesel production via transesterification (FAME) and hydrotreatment (HVO), combined heat and power (CHP), incineration, and polyhydroxyalkanoate (PHA)-based bioplastics (two process configurations). A gate-to-grave life cycle assessment (LCA) was coupled with environmental life cycle costing (eLCC) to internalise environmental externalities within the economic evaluation. Bioplastics and biodiesel (FAME) dominate the largest number of environmental impact categories, while CHP and incineration exhibit the lowest overall burdens. In terms of global warming, bioplastic routes display the lowest impacts (1.92-2.23 kg CO2-eq/kg UCO), whereas CHP, incineration and biodiesel routes exceed 3 kg CO2-eq/kg UCO due to combustion-related emissions. Microplastic impacts, despite affecting less than 5% of the material, are particularly relevant in the aquatic compartment. Economically, biodiesel (FAME) and incineration are the most favourable when only process costs are considered (1.21 €/kg biodiesel and 1.17 €/kg UCO). When environmental externalities are internalised, minimum selling prices increase substantially (up to 2.21 €/kg biodiesel), reversing the ranking. Overall, no route is clearly superior when environmental and economic performance are considered together, highlighting the need for policies and industrial strategies that account for environmental externalities to avoid burden shifting and promote sustainable UCO management pathways.