Physicochemical ammonia recovery and upcycling from wastewater: Advances from lab to implementation

Physicochemical routes for recovering and upcycling ammonia from wastewater are proliferating, yet deployment beyond the lab remains limited. This critical review interrogates the causes by synthesizing evidence across a broad range of technologies—adsorption, ion exchange, membrane contactors, electrodialysis, and electrochemical systems, with five representative technologies benchmarked within a unified framework covering Technology Readiness Level (TRL), selectivity in real matrices, energy and chemical footprints, product quality, and upcycling potential. No single pathway is universally optimal. A defining trade-off emerges: mature options (e.g., air stripping, conventional ion exchange; TRL 7–9) offer operational robustness but weak selectivity in complex wastewaters, yielding mixed-cation products of modest value, whereas more selective approaches (e.g., ligand exchange, bipolar-membrane electrodialysis; TRL 4–5) remain constrained by fouling, metal leaching, and uncertain long-term stability. Reported energy intensities span roughly two orders of magnitude (0.2–40 kWh/kg N), making grid carbon intensity a decisive yet underappreciated design variable. A synthesis of life-cycle assessments indicates environmental performance is system-dependent rather than technology-intrinsic, with electricity source and sulfuric acid inputs dominating impacts. We identify three barriers to implementation: the TRL–selectivity trade-off, a decentralization–centralization mismatch between distributed sources and concentrated markets, and overemphasis on removal efficiency over product value. To address these, we propose a context-driven, three-step decision framework—classify feeds, map TRL against selectivity and product quality, and embed prospective LCA early—supplemented by a hub-and-spoke logistics model to reconcile scale. While the proposed framework provides a structured approach for technology comparison, its application is subject to data availability and should be interpreted as indicative rather than prescriptive, particularly for emerging technologies lacking long-term operational validation. This guidance supports developers, utilities, and policymakers advancing circular nitrogen management.