Water flux increase by inverting the membrane from its normal position - Is it occurring in FO and PRO?

Flux increase occurs when a membrane is inverted from normal position of active layer (AL)-facing-feed solution (FS). It was noticed at the very early stage of reverse osmosis (RO) membrane development but much attention has not been paid since then, possibly because of severe internal concentration polarization that occurs in the porous sublayer. In forward osmosis (FO) and pressure retarded osmosis (PRO), when they are run in the preferred mode of AL-facing-draw solution (DS), the water flow direction is from the porous sublayer to the AL, which is the same as the inverted position of RO. Hence, it is interesting to know if a similar flux increase, from the normal to the inverted position, is also occurring in FO and PRO. The objective of this work is to confirm the effect of membrane inversion on the flux and separation of two RO membranes, as well as to know if a similar increase in water flux is occurring in FO/PRO. Results showed that significant flux increase, up to an order of magnitude, takes place when the membrane is in the inverted position, while exhibiting almost no selectivity. As for the possibility of such a flux increase in FO/PRO, it was denied by the multivariable regression analysis of the experimental FO/PRO data found in the literature.