A model-based analysis of water transport dynamics and fouling behaviors of osmotic membrane

Abstract

Water transport performance of forward osmosis (FO) has a crucial significance for successful implementations of the process in water and wastewater reclamation and seawater desalination. But, ascertainment of membrane fouling dynamics associated with simultaneous solute and water transfer still remains as one of the main research subjects for FO’s technological development. This study provides a deep insight to reveal the relations between water transport and membrane fouling propensities in FO by which model-based analysis was performed based on a novel osmotic resistance-in-series model developed for normal and reverse membrane orientations. Model results indicated that for the membrane operated with real seawater, osmotic water flux was mainly dependent on the active layer resistance regardless of orientation mode and osmosis time. Interfacial layer from effective draw interface by active layer/draw bulk interface, [dw−ma/db] seemed to be the main performance-limiting domain in which, as interfacial fouling increased, membrane permeated less water to draw. Predominant mechanisms were designated as homogeneous fouling of equivalent solute distributions and heterogeneous fouling of non-uniform nano-exclusion zones in normal and reverse modes, respectively. More interestingly, it was comprehended for reverse mode that the nature of nano-exclusion zones at the interface dw turned to a feature of uniform solute distributions at the interface ma/db. Very good agreements were found between experimental fluxes and theoretical results based on dimensional and dimensionless structural parameter and total resistances. After all, distinctive fouling behaviors clarified upon the adopted dynamics of transport were strongly verified by consistencies of high accuracy in the model estimations.