Fundamental mechanisms of three-component combined fouling with experimental verification

The present article describes a novel fundamental theory for investigating combined fouling by colloids (STXL), macromolecules, and solute ions (NaCl). Three macromolecules were used for the combined fouling study, bovine serum albumin (BSA), alginate, and dextran. The presented theory unifies singlet, doublet, and triplet fouling phenomena, including cake-enhanced osmotic pressure and binary colloidal fouling models, giving rise to the combined flux equation for three-component fouling assuming a completely mixed fouling layer. The predicted combined flux was compared to two equivalent fluxes calculated from individual foulant contributions. The strong form of the equivalent flux, known as the additive flux, was based on a linear superposition of flux decline due to individual foulants. The weak form of equivalent flux assumed stratification of individual foulant layers and hence a linear superposition of the individual fouling resistance. A comparison of experimental data and theoretical calculations revealed that the weak form of equivalent flux and the combined flux that was predicted by the novel theory provided the upper and lower limits, respectively, of the observed permeate flux. Furthermore, the model simulation results suggested a structural compression of the BSA gel layer, whereas such a compression did not occur in cases of alginate and dextran. The gel concentrations of alginate and dextran in the combined fouling layer seemed to be less than those in the macromolecular gel layer.