Nutrient Separation Systems: Current Progress and Future Opportunities.

As energy, environmental, supply chain, and economic risks escalate in today's linear fertilizer manufacturing processes, there has been growing interest in developing technologies that enable a circular nitrogen-based fertilizer economy. Achieving this goal requires significant advancements in wastewater treatment, with a specific focus on the design of technologies and complete systems that can capture and recycle waste nutrients into usable fertilizers. Every year, millions of tons of nitrogen and phosphorus remain untapped in global municipal and industrial wastewater, presenting a significant opportunity for fertilizer utilization. Herein, we explore current and future opportunities for nutrient recovery systems to provide recycled fertilizers for agricultural use. We first quantify recoverable nutrient wastewater sources, examine current nutrient management processes (e.g., nitrification-denitrification, EBPR), and highlight the performance and limitations of current nutrient management processes. We also review the current commercialization landscape for nutrient recovery systems and detail efforts made in advancing full-scale deployments. Finally, we review emerging electrified technologies and compare nutrient recovery technologies in terms of technology readiness, scalability, optimal feedstock, and environmental trade-offs, pairing them with optimal wastewater feed streams. A gap analysis is also conducted to guide future research and development efforts in nutrient recovery.