Abstract

Circular soil management represents a paradigm shift toward sustainable nutrient cycling, with phosphorus (P) and potassium (K) recovery from agricultural wastes emerging as critical components of resource-efficient farming systems. This comprehensive study evaluates P and K recovery technologies across 156 agricultural waste processing facilities in 23 countries, examining technical efficiency, economic viability, and environmental impacts. We analyzed recovery from livestock manure (64 facilities), crop residues (38 facilities), food processing wastes (32 facilities), and biogas digestate (22 facilities) using various technologies including anaerobic digestion, composting, pyrolysis, and chemical extraction. Results demonstrate that integrated recovery systems achieved P recovery efficiencies of 72-89% and K recovery efficiencies of 68-83% from organic waste streams. Anaerobic digestion coupled with struvite precipitation showed the highest P recovery (89 ± 7%), while thermochemical processing achieved superior K recovery (83 ± 6%). Economic analysis revealed break-even points at processing scales of 15,000-25,000 tons year⁻¹ for most technologies, with payback periods of 4.2-7.8 years. Recovered P and K products demonstrated comparable agronomic effectiveness to conventional fertilizers, with relative agronomic efficiency values of 85-95% for P and 82-92% for K across multiple crop trials. Life cycle assessment indicated 45-67% reduction in global warming potential and 52-74% reduction in eutrophication potential compared to conventional fertilizer production. Techno-economic modeling suggests that widespread adoption could recover 2.8-4.1 Mt P and 8.7-12.4 Mt K annually from global agricultural waste streams, representing 18-26% of current fertilizer P demand and 15-21% of K demand. However, implementation barriers include regulatory frameworks, market development, and technology standardization. Quality control challenges arise from heavy metal contamination (detected in 23% of recovered products) and pathogen presence (15% of facilities). This study demonstrates that P and K recovery from agricultural wastes can significantly contribute to circular soil management while reducing dependency on finite mineral resources and mitigating environmental impacts of waste disposal.