Selective Separations for Nutrient Circularity: From Molecular Insights to Field Implementation

Abstract Nutrient pollution remains one of the pressing water-quality challenges, leading to eutrophication, threats to aquatic life, and substantial remediation-associated costs. Simultaneously, concerns over phosphate depletion and the sustainability of chemical fertilizer production have intensified interest in valorizing nutrients from waste streams. Recent advances in adsorbents, membrane-based separations, and electrochemical processes have expanded opportunities for selective nutrient recovery. However, translating selective separations into implementation remains challenging due to variable nutrient speciation, matrix complexity, limited understanding of solid–water interfacial processes governing nutrient recovery, and uncertainties associated with long-term performance. These challenges are further compounded by the fact that a substantial proportion of nutrient losses originate from diffuse nonpoint sources, where nutrients are dispersed and viable recovery technologies remain limited. In this perspective, we examine the role of selective separations in advancing circular nutrient management and identify key scientific and engineering barriers that hinder implementation. We discuss opportunities to bridge laboratory-scale studies and field deployment through long-term performance evaluation and advanced synchrotron-based characterization capable of resolving nutrient–material interactions and degradation pathways. Finally, we highlight that the successful implementation of nutrient recovery technologies will depend on demonstrating environmental and economic benefits while fostering stakeholder and community participation.