A novel analysis of reverse draw and feed solute fluxes in forward osmosis membrane process

• A novel method to determine draw and feed solute fluxes in FO was developed.
• Draw and feed fluxes were not well predicted with the existing solute permeability.
• Apparent draw (Bd) and feed (Bf) solute permeability were proposed.
• Bd and Bf were applied to analyze draw solute loss and permeate water quality.

A novel method to determine reverse draw and forward feed solute fluxes in forward osmosis (FO) membrane was developed to analyze FO performance more accurately. Specifically, apparent draw solute permeability (Bd) and feed solute permeability (Bf) were proposed, instead of relying on single solute permeability (B). Our results clearly demonstrated that both draw and feed fluxes were not well predicted with the solute permeability (B) measured by RO mode experiment, typically employed in FO membrane characterization. In this study, the draw and feed solute permeabilities were evaluated independently by the experimental protocols which simulated actual FO operation more closely. Much better agreement between experimental observations and theoretical predictions was obtained when both Bd and Bf were applied for the analysis of draw and feed solute fluxes, respectively. Thus, the utilization of apparent draw and feed solute permeabilities provides more precise assessment of draw solute loss and permeate water quality, which are very important for FO membrane process design and operation.

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