Life Cycle Assessment of Municipal Biowaste Valorization in the EU: Environmental Impacts of Composting and Anaerobic Digestion with Biogas and Biomethane Production Scenarios

Sustainable management of the organic fraction of municipal solid waste (OFMSW) is essential for reducing environmental impacts and promoting resource recovery within a circular economy. This study applies life cycle assessment (LCA) to compare four biogas valorization scenarios in an integrated anaerobic digestion and composting system. A gate-to-grave boundary, a functional unit of one tonne of OFMSW, and the Environmental Footprint 3.1 method covering 16 midpoint impact categories are applied. The scenarios are combined heat and power (CHP) with useful heat recovery (S1), CHP without heat recovery (S1a), biomethane replacing natural gas for energy use (S2), and biomethane replacing natural gas used as a chemical feedstock precursor (S2a). Characterization, normalization, weighting, and contribution analyses identify environmental trade-offs and major impact sources. S1 has the lowest climate change impact (18.30 kg CO2 eq/t OFMSW), versus 46.60, 82.10, and 75.80 kg CO2 eq/t for S1a, S2, and S2a, respectively. S2a achieves the greatest fossil resource savings (−2,220 MJ/t OFMSW). EF 3.1 weighted single scores are 20.92 mPt (S1), 22.47 mPt (S1a), 22.53 mPt (S2), and 21.68 mPt (S2a), making S1 the best-performing option overall under the modeled conditions. Contribution analysis identifies digestate application to soil as a major environmental hotspot, especially for human toxicity and freshwater ecotoxicity, indicating the importance of downstream residue management. Overall, CHP with effective heat recovery offers the most favorable overall environmental performance, whereas biomethane use for chemical feedstock substitution conserves more fossil resources. These findings highlight the importance of evaluating biogas utilization within the complete waste treatment system and improving both energy recovery and digestate management to enhance OFMSW treatment sustainability.