Fouling of reverse osmosis and nanofiltration membranes by biological macromolecules - probing the foulant-membrane and foulant-foulant interactions

This study investigated the fouling of pressure‐driven membranes (reverse osmosis, nanofiltration, and ultrafiltration) and osmotically‐driven forward osmosis (FO) membrane by organic macromolecules. Protein and humic acid, two types of ubiquitous identified membrane organic foulants, were chosen as the model foulants. It was found that the hydrodynamic conditions (initial flux and cross‐flow velocity) and feedwater composition (foulant concentration, pH, ionic strength, and divalent ions concentration) played a significant role on the organic fouling of these two types of membranes. A limiting flux model is developed for predicting the fouling behavior of pressure driven membranes by organic macromolecules. The project investigated the dependence of limiting flux on intermolecular interaction between foulant molecules. It was observed that the limiting flux was directly proportional to the intermolecular electrostatic repulsive force and that conditions enhancing foulant‐deposited‐foulant repulsion resulted in greater limiting flux values. Such observations agree well with a theoretical model capturing both hydrodynamic and DLVO interactions. Interaction force measurements by atomic force microscopy (AFM) were also performed. The limiting flux correlated reasonably well with AFM interaction force between the model foulant and the fouled membrane surface.SUG 4/0