Harnessing algal biomass for biohydrogen production, algae-assisted microbial fuel cells, and environmental remediation: A waste-to-energy perspective

Algal biomass has attracted growing interest as a multifunctional platform for biohydrogen production and environmental remediation within circular bioeconomy and waste-to-energy frameworks. This review critically synthesizes recent studies on algal-biomass-centered hydrogen pathways, with emphasis on dark fermentation, photofermentation, sequential hybrid systems, and algae-assisted microbial fuel cells (MFCs). Reported hydrogen yields from pretreated algal hydrolysates generally range from 8 to 14 mmol H₂ g⁻¹ volatile solids in dark fermentation. At the same time, sequential dark-photo systems can improve overall carbon recovery under optimized laboratory conditions. Algae-assisted MFCs typically achieve power densities of about 0.3–1.2 W m⁻² together with high nutrient-removal efficiencies and substantial Chemical Oxygen Demand (COD) reduction. In parallel, algal systems offer environmental benefits through wastewater polishing, carbon assimilation, and the valorization of residual biomass. The review does not attempt to cover all hydrogen production routes; rather, it focuses on pathways in which algal biomass acts as the direct substrate or functional biological component. Major barriers remain in harvesting energy demand, process variability, gas purification, and limited pilot-scale validation. Overall, algae-based systems represent promising but still pre-commercial platforms for integrating renewable fuel generation with remediation and resource recovery.