Abstract
Municipal wastewater treatment plants (WWTPs) are potential sites for decentralized water electrolysis because they combine water availability, operational infrastructure, and local integration options for electrolysis coproducts. This review evaluates three downstream pathways for electrolytically produced gaseous hydrogen (H2): onsite energetic use, trailer-based compressed gaseous H2 export, and pipeline-based delivery. The system boundary extends from the H2 handover point downstream of the electrolyzer to the WWTP-side utilization or transfer interface. A process-chain-based techno-economic synthesis identifies pathway-specific technical functions, interfaces, and cost-relevant components, including gas conditioning, compression, storage, reconversion, transport infrastructure, metering, control, and safety systems. For onsite use, PEMFC operation is associated with flexible, electricity-oriented reconversion, whereas the investigated modular H2 CHP configuration represents comparatively steady cogeneration with simultaneous electricity and heat supply. For trailer-based export, compression, storage configuration, payload, utilization, and transport distance are key technical and economic drivers. For pipeline delivery, throughput, distance, pressure management, and pipeline sizing determine system performance. A directly comparable transport study indicates that trailer-based delivery is favored at lower H2 throughputs, whereas pipeline transport becomes more favorable at higher throughputs, with the crossover strongly dependent on transport distance. The synthesis supports site-specific assessment of gaseous H2 utilization pathways in WWTPs.