Unraveling Organic Fouling in Membrane Distillation: In Situ Dynamics, Predictive Modeling, and a Self-Limiting Regime

Organic fouling poses a primary barrier to the widespread application of membrane distillation (MD), an emerging technology for treating high‑salinity and chemically complex wastewaters. Despite its importance, quantitative insight into fouling dynamics remains limited, hindering the development of effective mitigation strategies. Here, we monitored the fouling dynamic using optical coherence tomography (OCT) and quantified this dynamic with an extended collision–attachment model. Results indicated that the model showed excellent agreement with experimental observations ( R 2  = 0.95), accurately capturing the kinetics of both foulant deposition and flux loss. With the model, we successfully identified and quantified the key factors governing the fouling dynamics. Notably, our analysis reveals that, in contrast to pressure-driven membrane processes where hydraulic resistance dominates, flux loss by organic fouling in MD is primarily governed by cake-enhanced temperature polarization. Based on these findings, we proposed a framework that enabled both qualitative analysis of organic fouling control strategies and quantitative description of their effects on fouling dynamics, and identified a self‑limiting regime in fouling dynamics, which was attributed to the feedback between collision-attachment kinetics and cake-enhanced temperature polarization effects. This work offers a theoretical basis for the optimization of MD processes and the development of fouling mitigation strategies.