Human urine as a new-gen fertilizer for sustainable agriculture: a review towards a circular nutrient economy

The energy-intensive production and environmental repercussions of synthetic fertilizers pose significant challenges to agricultural sustainability. Nutrient recovery from human urine, an underutilized renewable resource rich in nitrogen (N), phosphorus (P), and potassium (K), offers a low-energy pathway that supports the Sustainable Development Goals (SDGs 6 and 12). This review synthesizes global research on human urine-based fertilization as a sustainable alternative to synthetic inputs using a systematic approach guided by PRISMA 2020 standards. Additionally, bibliometric analysis and techno-agronomic evaluation were performed on 123 peer-reviewed articles published between 2011 and 2025. Key urine stabilization and nutrient recovery technologies, including source separation, membrane filtration, electrodialysis, ion exchange, bio-electrochemical systems and biochar adsorption, are critically assessed. The nutrient recovery efficiencies ranged from 50-95% for N, 40-99% for P, and 80-98% for K, depending on stabilization method and recovery pathways. Agronomic evidence indicates that urine-derived fertilizers can match or exceed mineral fertilizers, with yield improvements of 10-70% compared to unfertilized controls and yields comparable to urea when applied at equivalent N rates. However, major challenges include membrane fouling, energy requirements, odor issues, and the persistence of pharmaceutical contaminants. Unlike earlier reviews that focused mainly on ecological sanitation or individual recovery technologies, this review integrates PRISMA-based systematic screening with bibliometric mapping and comparative techno-agronomic synthesis. It emphasizes research trends, performance indicators, soil health effects, and scalability barriers, providing a comprehensive evidence-based framework to support the adoption of urine-derived fertilizers within a circular nutrient economy.