Beyond the flush: a review of wastewater circular systems

Global freshwater scarcity and degradation demand reconceptualizing wastewater as a resource within circular economy transitions. This review utilizes the resource-stack model and treatment-train design space to evaluate wastewater valorization, assessing recovery of water, energy, nutrients, carbon, and trace elements. It examines barriers, inefficiencies, costs, regulatory gaps, and societal resistance and highlights that aligning innovation with policy and governance can transform wastewater systems into infrastructures supporting water security and climate resilience.