A model of membrane fouling by salt precipitation from multicomponent ionic mixtures in crossflow nanofiltration

A coupled model of concentration polarization, ion transport in membrane pores, and fouling by salt precipitation is used to predict the permeate flux decline due to scaling during crossflow nanofiltration of a multicomponent ionic mixture. The model considers a fouling layer buildup due to salt. precipitation once the solubility product of the sparingly soluble salt in an ionic mixture is exceeded. The precipitated salt deposits on the membrane surface, and reduces the permeate flux through the membrane. The primary novelty of the presented methodology is its ability to predict the local fouling behavior at different axial positions in a crossflow filtration channel. Using the model, we assess the fouling behavior of a ternary mixture of Na2SO4 and CaSO4 for various feed concentrations, pertinent membrane properties, and operating conditions to predict the axial location in a crossflow filtration channel where scaling due to calcium sulfate precipitation will initiate. Simulations for a four-component mixture (Na2SO4/CaCl2) are also performed to depict the fouling behavior in a complex ionic mixture closely resembling feed waters used in membrane treatment operations.