A Semi-Quantitative Method for Prediction of the Rejection of Uncharged Organic Micropollutants with Nanofiltration

A method for predicting the rejection of uncharged organic pollutants with nanofiltration, based on solute-membrane interactions affecting this rejection and on readily available knowledge about solute- and membrane parameters, was developed. Rejection values of model organic contaminants were measured with bench-scale NF experiments, using Trisep TS80-TSF membranes. Organic contaminants were subdivided into different categories, based on their hydrophobicity (expressed as log Kow-value). Predicted rejection curves, modeled with a log-normal model based on the molecular weight of the solutes, were in close agreement with the experimental data for the different categories of solutes. However, large differences were found between rejection curves for hydrophilic and hydrophobic molecules: rejection curves for hydrophobic molecules have an inflection point at higher molecular weight values compared to hydrophilic molecules and the incline of the rejection curves is less steep for hydrophobic molecules compared to hydrophilic molecules. This indicates that hydrophobic and hydrophilic solutes demonstrate different molecular weight cut-off values on a single membrane and that hydrophobic-hydrophobic interactions between solute and membrane affect rejection of hydrophobic solutes, while rejection is mainly a sieving phenomenon for hydrophilic solutes.