Membrane interactions with NOM and an adsorbent in a vibratory shear enhanced filtration process (VSEP) system

The effects of torsional membrane vibration and the addition of heated aluminum oxide particles (HAOPs) on the interactions of natural organic matter (NOM) with UF membranes were investigated using a vibratory shear enhanced filtration process (VSEP) laboratory module. Torsional vibration reduced fouling in both dead-end and crossflow modes. Incorporating crossflow into a system with vibration increased NOM removal efficiency. In systems with crossflow, increasing the vibration amplitude decreased fouling up to a point, and provided negligible benefit thereafter. On the other hand, it had a negligible effect on NOM rejection up to the same point, and improved permeate quality thereafter. Although a mass balance suggested that a negligible portion of the NOM remained on the membrane surface at the end of the crossflow tests, foulant aggregates were observed on the membrane both visually and in SEM images. The SEM images indicated that vibration changed the morphology of the foulants from a continuous layer into scattered clumps, and that higher vibration amplitude facilitated this transformation. Deposition of a HAOPs layer on the membrane surface relieved fouling only initially, after which the HAOPs/UF system fouled almost as fast as a bare UF membrane. However, intermittent vibration to re-mix HAOPs particles during the HAOPs/UF operation kept permeate flux relatively high for much longer, thereby significantly improving the performance.