From Waste to Wheels: a Life Cycle Assessment of Manure-based Biomethane for Decarbonizing Transportation in Current and Future Scenarios for Argentina

Purpose. The purpose of this study is to quantify the life cycle environmental impacts of biomethane from cattle manure used in passenger transportation in Argentina, comparing fossil natural gas, biomethane, and biomethane with carbon capture and storage (CCS) under current conditions and 2050 prospects. The study addresses the following research question: can biomethane provide a net reduction in greenhouse gas emissions without significant burden-shifting in other impact categories? Methods. A cradle-to-wheel LCA was conducted using Brightway2 and the ecoinvent v3.10 database. Background processes were modified using the premise tool to incorporate IMAGE, REMIND, and TIAM-UCL IAM projections for the year 2050 (SSP2 RCP-2.6 pathway). The functional unit was 1 km driven by a passenger in a car. Scenarios included natural gas, biomethane from cow manure, and biomethane with CCS, both with and without avoided emissions from digestate substituting synthetic fertilizer. Impact categories were assessed using ReCiPe2016 midpoint characterization and USEtox human and ecotoxicity metrics. Sensitivity analyses examined manure transportation distance. Results and discussion. Under current conditions, biomethane coupled with CCS could reduce global warming potential by 43.5% to 73.2% relative to natural gas (from 0.117 kg CO₂-eq/km to 0.056 kg CO₂-eq/km) and depending on the distance manure is transported, with net-negative values achieved when urea substitution credits are applied. However, eutrophication and acidification increase due to manure transportation and digestate application, while toxicity indicators rise with the higher energy demand of upgrading and CCS. Prospective scenarios for 2050 projected further GWP reductions of up to 80% (e.g. in the TIAM-UCL scenario) driven by decarbonized energy systems, but toxicity burdens intensified under deeper electrification pathways. Key hotspots include methane leakage, grid emissions, and digestate management. Conclusions. Manure-derived biomethane, particularly when coupled with CCS, offers significant climate benefits for Argentine transportation, but may shift impacts to eutrophication, acidification and toxicity categories. Full carbon neutrality requires reducing methane leaks, decarbonizing electricity inputs, and optimizing digestate use. Policymakers and industry should promote decentralized digesters near livestock operations to lower manure transport emissions, supply renewable energy for upgrading and CCS, and use best digestate practices to minimize eutrophication and acidification while maximizing fertilizer substitution benefits.