Application of low frequency transverse vibration on fouling limitation in submerged hollow fibre membranes

Dynamic membrane systems provide highly turbulent flow regimes close to the membrane surface. In this work, flux enhancement of submerged hollow fibre membrane system was achieved by imposing rotationally oscillating fluid or transverse oscillating membrane motion. The transverse vibration in the system generates the shear as well as secondary flows, contributing to fouling limitation even at low displacements (<5 mm) and frequencies (<21 Hz). Transverse vibration limits cake formation by focusing shear forces more directly on the membrane surface rather than recirculating the bulk fluid. The substantial benefits of transverse vibration on fouling limitation were observed in terms of critical flux improvement for macromolecular (alginate), particulate (yeast, bentonite) and anaerobic bioreactor solutions for 0.04 μm polyvinylidene fluoride membrane. However, lower fouling limitation was observed for alginate with the more permeable 0.2 μm polypropylene membranes, for which the alginate rejection was low and internal pore blocking was likely to occur. Even for a solution with high concentration (200 g/L yeast) and high viscosity, low transmembrane pressures were maintained at modest fluxes with the aid of transverse vibration. During the filtration of supernatant from an anaerobic bioreactor, filtration with transverse vibration showed better fouling control compared with traditional fouling limitation methods such as periodical backwash or relaxation. Correlations for inertial and drag force for single oscillating cylinder were used to provide preliminary estimates of the energy requirements to generate the transverse vibrations in defined frequencies and displacements.