Effect of shear rate on fouling in a Vibratory Shear Enhanced Processing (VSEP) RO system

Membrane fouling due to formation of inorganic scales limits the application of reverse osmosis (RO) technology for desalination. This study continued our investigation of the performance of RO membranes in a Vibratory Shear Enhanced Processing (VSEP) system during the treatment of a simulated brackish water source and a brine. Increasing vibration amplitude decreased membrane fouling, increased rejection of most solutes and changed the morphology of the scales from a tightly packed layer to a more scattered distribution of particles that is easier for water to permeate. Decreasing pH reduced fouling slightly, and the presence of natural organic matter displayed no substantial effect. When all but a thin ring of the membrane surface was sealed by impermeable epoxy resin, fouling decreased as the shear rate increased. In these tests, the fouling rate was almost identical in paired tests in which the same average shear rate was achieved by different combinations of ring radius and vibration amplitude. The shear rate appears to control fouling by determining the structure of the scale deposit that forms early in a filtration run.