Hydrogen production from municipal solid waste: Thermochemical and biochemical pathways, microbial ecology, and the case for an integrated hybrid biorefinery

This study presents a structured review of municipal solid waste (MSW) valorization technologies for hydrogen production. MSW is a promising feedstock because it simultaneously reduces waste accumulation and generates low-carbon fuel. Hydrogen production from MSW involves multiple pathways rather than a single technology. Thermochemical routes are suitable for mixed or dry waste, while biochemical routes mainly target organic fractions such as food waste. Major technologies, including gasification, steam gasification, pyrolysis-steam reforming, dark fermentation (DF), photo fermentation (PF), and microbial electrolysis cells (MECs), are evaluated based on performance, scalability, and feedstock compatibility. Thermochemical routes generally produce 40–43 g H₂/kg MSW, with optimized co-gasification reaching 66–71 g H₂/kg and steam gasification achieving up to 79.8 vol% H₂ under catalytic conditions. Biochemical routes operate under milder conditions but yield lower hydrogen production, typically 9–14 g H₂/kg volatile solids, while two-stage systems produce approximately 12–16 g H₂/kg food waste. Key optimization factors, including pH, temperature, pretreatment, and organic loading rate, are discussed alongside emerging tools such as nanotechnology and synthetic biology. A hybrid biorefinery concept is proposed, directing wet organics to biological conversion and dry fractions to thermochemical processing, potentially achieving 28–50 kg H₂ per ton of MSW. This integrated framework links feedstock-specific pathways, challenges, and opportunities to support scalable and sustainable MSW-to-hydrogen systems within circular economy and decarbonization strategies.