Hydrogen production from water industries for a circular economy

The ever-increasing global energy crisis, environmental degradation and climate change issues impacted by excessive consumption of fossil fuels (FFs) are pushing the world to find a suitable and green energy source for ensuring net-zero emissions and attaining the sustainable development goals (SDGs)-6, 7 and 13 through decarbonization of the global energy system (GES). Green hydrogen has been considered one of the most groundbreaking aspects of low-carbon future energy security. Integration of water industries (WI) and circular economy (CRE) perspectives can be crucial to green energy production and sustainable resource management. This study comprehensively and critically assesses the role of WI in hydrogen production (HP) from a CRE perspective. The current scenarios of global energy production, consumption patterns linked with CRE, and the necessity of a worldwide energy transition from FFs to a hydrogen economy (HE) have been discussed constructively. The structures of WI and its function have been proposed for the first time connecting the requisite of CRE. Moreover, a detailed bibliometric assessment of HP technologies has been conducted. In addition, the HP technologies in WI have been described in-depth with their suitability, advantages, and drawbacks. An all-inclusive techno-economic and environmental feasibility study of the HP technologies in WI and the latest case studies have been conducted. Furthermore, the scaling-up challenges of HE in WI have also been assessed. This paper is the first integrated approach to evaluating the HP technology's suitability in WI from a CRE point of view which will provide significant insights to develop a future HE.