Frontier research progress on the separation of source-separated urine by membrane distillation technology

Membrane distillation (MD) faces significant challenges in treating source-separated urine due to severe membrane scaling driven by dynamic chemical evolution, primarily due to urea hydrolysis. To clarify the coupling between urine-specific chemistry, scaling mechanisms, and MD operation, this review synthesizes recent progress. It establishes that the elevated pH and ammonia formation from hydrolysis create high interfacial supersaturation, which triggers an autocatalytic scaling pathway dominated by secondary nucleation-a key mechanistic distinction from treating compositionally stable feeds. A central operational insight is the critical role of feed temperature and heating duration in controlling ammonia volatilization and scaling kinetics. Building on this mechanistic understanding, the review consolidates synergistic strategies for performance enhancement, including operational optimization, membrane modification, module design, and hybrid processes. These insights provide essential theoretical guidance for the rational design of MD systems aimed at efficient nutrient and water recovery from urine.