Engineered pathways for multimodal hydrogen production from wastewater: A comprehensive review on the mechanisms and metrics of efficient recovery systems

The use of hydrogen is steadily expanding beyond traditional sectors like refining and ammonia synthesis, with increasing demand in energy storage, aviation fuel and power generation sectors. Despite hydrogen being positioned as the growing solution for the global climate crisis, a growing body of literature highlights the challenges pertaining to conventional hydrogen production. Low emission hydrogen accounted for less than 1% of total global H2 produced in 2023, fuelling the need to find production means compliant with sustainable and circular economy directed principles. Taking this into consideration, waste-to-hydrogen strategies present a feasible solution that not only mitigates the problems of waste disposal, but also aids in the efficient generation of clean energy, as the ability of these technologies to convert around 40-60% of energy into useable hydrogen with carbon conversion efficiencies ranging between 70 and 90%, offer 60-70% lower net carbon emissions over traditional methods. The novelty of this article lies in its integration of techno-economic analysis (TEA) and life cycle assessment (LCA) parameters to systematically evaluate the performance of multimodal hydrogen recovery systems and provide a quantitative basis for the analysis of overall practicality and sustainability of waste-to-hydrogen systems. Further, the focus of this review is centred around providing a thorough exploration into various waste-to-hydrogen systems with key emphasis on their critical process features and underlying mechanisms.