Abstract
The objective of this study is to quantitatively model the pH effect on sodium chloride rejection by commercial reverse osmosis membranes. The objective was achieved by measuring the charge density of the polyamide active layer at pH of interest and taking into account the Donnan exclusion effect in the solution/diffusion-advection theory. The experimental and modeling results showed that the predicted chloride ion rejection at pH 10.4 was in good agreement with the experimentally measured values for the ESPA3 membrane with a homogeneous active layer. However, the prediction based on surface charge density overestimates chloride ion rejection for the ESPA2 membrane, which has a heterogeneous active layer. This result demonstrated the need for developing a new solute transport model the considers the heterogeneity of active layers.
