Enhancing Urea Recovery and Hydrolysis Inhibition from Source-Separated Urine through a Novel Urea Electric-Assisted Forward Osmosis System: Insights from Reaction Kinetics and Mechanisms

The efficient recovery of urea from human urine, where it is abundant, not only facilitates resource utilization but also mitigates potential environmental pollution. This study developed a novel urea electro-assisted forward osmosis (UEFO) system to recover urea from source-separated urine, aiming to enhance urea recovery efficiency and suppress urea hydrolysis through the synergistic interaction between the electric field and FO. The UEFO leveraged the application of an electric field to facilitate ion migration and in situ OH^- generation, enabling dynamic regulation of the osmotic pressure difference. This enhanced the urea recovery and stabilized alkaline conditions. Compared with the open-circuit system, the UEFO significantly improved urea recovery efficiency and transport kinetics. Meanwhile, the UEFO significantly enhanced the alkalinity of the feed solution through the in situ OH^- generation, thereby reducing urease activity by 34.73%. Additionally, partial least squares path modeling revealed that the electric field was the critical driving factor for urea recovery in the UEFO. Contribution distribution revealed that the electric field contributed 59.41% to urea recovery and 79.29% to hydrolysis inhibition, highlighting its key role as the core driving force in UEFO. Mechanistic exploration revealed that the electric field dynamically regulated the osmotic pressure difference across the FO membrane by modulating ion migration and the chemical environment, thereby promoting efficient urea migration and inhibiting its hydrolysis. Furthermore, an economic assessment demonstrated that the use of UEFO could generate a net profit of $0.34 per ton of urine treated, achieving a positive economic return. This study provides an innovative solution for urea recovery from source-separated urine, offering critical scientific and technological support for the development of sustainable nitrogen resource recycling technologies.