Implications of the Membrane-Independent Limiting Flux In Forward Osmosis

Forward osmosis (FO) represent a low-fouling alternative compared to pressure-driven membrane processes, particularly as a pretreatment step for challenging feed waters. Thus, in practical applications, FO membrane fouling is anticipated. This work demonstrates for the first time that a membrane-independent limiting flux exists with fouled FO membranes. While the limiting water flux reaches a maximum value that cannot be overcome by increasing the draw solution osmotic pressure, reverse salt flux continually increases. Thus, there is a drawback when excessive osmotic pressures are applied. These results suggest that future FO developments should focus on operating parameters and fouling mitigation rather than membrane properties.