Fouling of RO membranes in a vibratory shear enhanced filtration process (VSEP) system

Fouling induced by inorganic scaling is a major challenge limiting the use of reverse osmosis (RO) technology in many water treatment applications. This fouling can be reduced by using torsional vibration of flat sheet membranes to induce high shear rates at the membrane surface. We investigated fouling of RO membranes using a vibratory shear enhanced filtration process (VSEP®, New Logic Research, Emeryville, CA) system to treat a simulated brackish water source and a brine. Vibration substantially reduced membrane fouling and increased practical water recovery from 80% to over 90% for the brackish solution and from 50% to 75% for the brine. When the membrane was vibrated, fouling accounted for a much smaller fraction of the total hydraulic resistance during treatment of both the brackish solution and the brine. Vibration also increased rejection of major ions from between 70% and 88% to >95% in the brackish solution and >90% in the brine. SEM images indicated that vibration changed the morphology of the surface scale from a uniform layer of needle-like solids to a smoother layer that was apparently more hydraulically conductive. This morphological change seemed to increase the overall volumetric flux by opening up areas on the membrane surface that were otherwise covered by scales.