Characterization and identification of rejection mechanisms in nanofiltration membranes using extended Nernst–Planck model

Abstract

Nanofiltration (NF) membranes have found increasing applications especially in water and wastewater treatment. In order to predict and optimize the performance of NF membranes, the membranes need to be characterized properly in terms of their structural parameters such as pore radius (r p) and effective thickness (Δx/A k) as well as the effective charge density (X d). In this work, three cellulose acetate NF membranes were fabricated to different properties and were characterized using a model based on the extended Nernst–Planck equation. The results show that the variations of r p, Δx/A k and X d are quite distinct between the three membranes. The membranes were found to have r p>1.2 nm and high X d. Thus the rejection mechanism depends very much on the Donnan effect rather than the steric effect. The high rejection of several negatively charged organics and salts confirmed this finding. Apart from being effective, this method of characterization offers a cheaper alternative in understanding NF membranes.