Electrochemical recovery of nutrients from human urine coupled with biogas upgrading

This study explored the coupling of electrochemical nutrient recovery from human urine with biogas upgrading. Ammonia nitrogen-rich (≥300 mM) and alkaline (≥pH 9) hydrolyzed urine (HU) is a promising alternative CO₂ solvent. Spent urine after biogas upgrading (SU), with neutralized pH and increased conductivity resulting from CO₂ absorption, is advantageous over HU for recovering total ammonia nitrogen (TAN) through electro-concentration. Experiments using synthetic urine at varying applied current densities (13-77 A/m²) demonstrated effective TAN recovery from both HU and SU, with greater enrichment factors at higher currents (2.1-3.3-fold, 1.2-1.8 M TAN concentrate). Validation experiments using real urine at the optimized current density of 52 A/m², considering energy consumption, exhibited superior TAN recovery and energy efficiency when using SU (3.7-fold enrichment, 1.6 M TAN concentrate; suitable for liquid fertilizer) compared to HU. These findings offer an advanced strategy for maximizing urine valorization, contributing to a circular economy.