Closing the loop in organic municipal solid waste composting: Environmental assessment of leachate-to-energy pathways

Composting is widely applied for managing the organic fraction of municipal solid waste (OFMSW), however, its environmental performance is strongly dependent on process design and the management of by-products, particularly compost leachate, which is often neglected in life cycle assessments (LCAs). This study conducts a comparative LCA of a large-scale windrow composting facility in India, with explicit consideration of leachate as a resource for energy recovery. Three scenarios were evaluated per tonne of OFMSW: (i) composting without energy recovery, where leachate is utilized as a liquid fermented organic manure substitute; (ii) composting with anaerobic digestion of leachate and subsequent biogas-to-electricity generation; and (iii) composting with leachate-derived biogas upgraded to compressed biomethane (CBG) for vehicle fuel. Environmental impacts were assessed using the ReCiPe 2016 (H) method. The modelled results indicate that integrating leachate-based energy recovery has the potential to improve the environmental performance of composting systems under the assumptions considered. The biogas-to-electricity pathway showed the lowest global warming (−17.9 kg CO 2 eq. ton −1 ), followed by the baseline scenario (−1.43 kg CO 2 eq. ton −1 ), while the CBG pathway approached near-neutral emissions (0.49 kg CO 2 eq. ton −1 ). Across all scenarios, fertilizer substitution from compost and leachate-derived manure was the dominant contributor to environmental benefits. Sensitivity and break-even analyses identified compost utilization rate, transport distance, and biogas yield as critical parameters. The findings indicate that integrating aerobic OFMSW composting with anaerobic digestion and valorization of the generated leachate could enhance environmental performance and support circular resource utilization when the assumed treatment and resource-substitution conditions are achieved.