Municipal solid waste to hydrogen: thermochemical pathways, carbon-negative potential, and AI-driven optimization toward circular energy systems

The thermochemical conversion of municipal solid waste (MSW) into hydrogen offers a promising pathway for simultaneously addressing waste management and producing low-carbon energy carriers. This review provides a c omprehensive and critical assessment of MSW-to-hydrogen production through gasification and pyrolysis by integrating recent advances in experimental studies, process modelling and simulation, techno-economic analysis (TEA), life cycle assessment (LCA), artificial intelligence (AI)-driven optimization, and technology readiness. Unlike previous reviews that primarily examine these topics independently, this work systematically connects feedstock characteristics, thermochemical performance, process simulation, economic feasibility, environmental sustainability, and digital optimization within a unified framework. Among thermochemical routes, gasification remains the most mature technology, typically operating at 800-1100°C and producing hydrogen-rich syngas with reported hydrogen concentrations of 39-51 vol.%, while advanced catalytic and sorption-enhanced gasification has achieved hydrogen concentrations of up to 80.76 vol.% under optimized experimental conditions. Comparative TEA studies indicate that hydrogen production costs are primarily governed by electricity price, plant capacity factor, gate fees, and carbon pricing rather than conversion technology alone. LCA results consistently demonstrate lower greenhouse gas emissions than conventional steam methane reforming, with carbon-negative performance reported only under specific assumptions, including carbon capture and storage (CCS), avoided landfill emissions, renewable electricity, and biogenic carbon accounting. Recent advances in AI, machine learning, and digital twins further demonstrate significant potential for improving process prediction, feedstock management, real-time optimization, and integrated sustainability assessment. Overall, MSW-to-hydrogen systems represent a technically feasible and environmentally attractive pathway toward circular energy systems. However, large-scale commercialization still requires improved feedstock standardization, contaminant management, gas cleaning, hydrogen purification, reactor scale-up, harmonized TEA-LCA methodologies, and greater integration of AI-enabled digital technologies.