Can WWTPs become biorefinery centers for producing green hydrogen? A simulation case integrating sludge gasification and water electrolyzers

Wastewater treatment plants (WWTPs) can serve as hubs for converting waste into energy, thereby supporting a city's energy needs. Sewage sludge can be converted into valuable products through thermal processes. In gasification, energy-rich syngas is produced, which can be further valorized to generate electricity. However, the use of air introduces nitrogen as a diluent, thereby reducing the energy density. Integrating electrolyzers for hydrogen production into the process offers an added advantage: the use of oxygen as a gasification agent, thereby reducing dilution. The present work assesses the simulation of a conventional WWTP using Superpro Designer V13. Using pure oxygen in the gasification unit reduces the thermal energy requirements of the process. It increases the energy content by 4% when the system is operated under a CO2 atmosphere and a 25% equivalence ratio (ER: 4.0) for both cases. Water electrolysis is integrated as an energy storage system; therefore, the scenarios analyzed assumed intermittent hydrogen production. This document highlights the importance of advancing research on the use of reclaimed water for hydrogen production, as well as the efficient integration of processes to reduce the energy and water footprints of technologies supporting a green transition.