Waste-to-biohydrogen production technologies: Microbial pathways, omics insights, and techno-economic assessment for a circular hydrogen economy

• Microbial processes provide sustainable routes for BioH 2 production • Dark fermentation, photofermentation, and biophotolysis are key pathways • Wastewater is a cost-effective dual feedstock for BioH 2 generation • Multi-omics tools improve microbial yield and system optimization • Techno-economic analysis supports large-scale industrial application Among emerging green hydrogen (H 2 ) production strategies, microbial biohydrogen (BioH 2 ) technologies represent promising low-carbon and waste-valorization pathways. This review presents a comprehensive analysis of waste to H 2 production systems within a circular H 2 economy framework. A bibliometric assessment first maps research trends, thematic evolution, and global scientific dynamics in microbial BioH 2 production. The review then examines solid biomass pretreatment technologies (physical, chemical, and biological) as critical steps for efficient substrate conversion, followed by fermentative, enzymatic, and photosynthetic production routes, highlighting key microbial catalysts and metabolic pathways. The valorization of wastewater streams is further explored, emphasizing their dual function in renewable H 2 generation and environmental remediation. Advances in genetic engineering and multi-omics approaches are critically discussed for their role in enhancing H 2 yields, optimizing microbial consortia, and unraveling regulatory networks governing H 2 metabolism. Finally, environmental sustainability, techno-economic feasibility, and downstream H 2 storage and distribution challenges are evaluated to identify barriers and development pathways for large-scale implementation of waste-derived BioH 2 systems.