Trends and errors in reverse osmosis membrane performance calculations stemming from test pressure and simplifying assumptions about concentration polarization and solute rejection

Removal of heavy metals from wastewater using reverse osmosis

“…The data from the other studies focused on permeate flux and solute release. The study by Armstrong et al (2022) on the SWC4 seawater membrane and an ESPA3 brackish water membrane showed that membrane performance is evaluated on water-solute selectivity depending on the pressure applied during permeation tests. Qi et al (2016) also found that water permeability and solute rejection are sensitive to temperature and applied pressure.…”

The Adverse Effect of Concentration Polarization on Ion–Ion Selectivity in Nanofiltration

“…While solute–solute selectivity in NF membranes is primarily governed by the intrinsic interactions between the transported solutes and the membrane, − the operating conditions and solution composition may also play roles in the ability of the membrane to achieve selectivity. , Specifically, accumulation of rejected solutes on the membrane surface due to the laminar (near no-slip) flow conditions adjacent to the surface results in the so-called concentration polarization (CP) effect, − which increases the transmembrane driving force of different solutes to varying extents, affecting the selectivity. − Whereas the detrimental effect of CP has been extensively discussed in the context of promoting irreversible fouling, , inducing scaling, and increasing the energy consumption of membrane systems, the impact of CP on the selectivity between solutes has been given less attention. Notably, since CP is more prominent for larger solutes with lower diffusivity in water (i.e., the diffusivity dictates the solute ability to “escape” from the surface), which are usually better rejected by the membrane, the overall effect of CP is to improve more the permeation of these solutes compared to smaller, more permeable solutes, resulting in reduced selectivity.…”