Valorising co-produced oxygen from green hydrogen systems: circular economy pathways in wastewater treatment

Abstract

Population growth, climate change, and urbanisation significantly contribute to environmental stress, particularly through the depletion of finite resources like clean, easily accessible freshwater. In the water industry, the supply chain must become more independent, shifting from the prevailing linear delivery model to a circular economy. This shift can be achieved by adopting advanced treatment methods to ensure high-quality treated water and minimising waste and emissions. A transition to a circular economy can offer an opportunity to address sustainability issues in multiple sectors. For example, the water and energy nexus recognises that these two sectors are inextricably linked. Integrating green hydrogen production and wastewater treatment (WWT) has been identified as a promising strategy as part of the water-energy nexus, which advances the circular economy. When the green hydrogen economy uses treated wastewater as a feedstock, contributing to water reuse, the water industry can further enhance the sustainability of this approach by utilising co-products from hydrogen synthesis, such as high-purity oxygen. This oxygen can then be employed in various stages of WWT, including aeration and producing key reagents such as ozone and hydrogen peroxide, aiming to improve treatment efficiency and reduce emissions. Accordingly, this study examines how such applications can enhance circularity within the water sector. The principal findings were: (i) integrating green hydrogen production with WWT offers promising environmental and economic benefits but requires deeper technical, regulatory, and stakeholder alignment; (ii) optimising co-product oxygen utilisation in aeration and advanced treatment can help enhance WWT performance and economic viability; (iii) future research should prioritise techno-economic assessments, pilot-scale demonstrations, and system-wide integration studies to enable successful implementation of this circular and sustainable approach.