Current global state of hydrogen production through dark fermentation of agricultural residues: A state-of-the-art review

Increasing global energy demand, depletion of fossil fuels, and concerns regarding environmental pollution have shifted global priorities toward developing clean biohydrogen production systems, particularly through dark fermentation of agricultural biomass residue. However, the recalcitrant and heterogeneous nature of agricultural biomass limits microbial access to fermentable carbohydrates. This review synthesises continental data on residues from major crops and evaluates their utilisation for dark-fermentative biohydrogen production. Published assessments project that residues from major crops could yield approximately 15.5 Mt H 2 yr −1 globally by 2030. Asia has the greatest feedstock potential; in China alone, available crop residues have been estimated to support approximately 30.15 billion m 3 H 2 yr −1 , equivalent on an energy basis to 11.48% of China's natural-gas consumption and 1.95% of its coal consumption in 2019. The review further describes the advances in pretreatment technologies for agricultural biomass residue aimed at achieving high-yield sugar recovery. Additionally, it evaluates the toxicity of biomass-derived inhibitors and highlights key strategies to mitigate their adverse effects during the microbial biohydrogen production process. The insights provided in this review will contribute to the effective and sustainable utilisation of agricultural biomass residues for biohydrogen production, to support a biocircular economy, improve global energy security and thus mitigate climate change driven by excessive fossil fuel utilisation. However, realising this potential will require sustainable residue recovery, efficient pretreatment, inhibitor control, and successful process scale-up.