Particle oscillation at corrugated membrane-water interface: An in-situ direct observation and implication to membrane fouling control

Abstract

Membrane surface patterning is an emerging technique for membrane fouling control. However, the underlying mechanism for this technique has not been well understood due to the lack of direct evidence on the flow field and the associated contaminant transport at the membrane-water interface. Therefore, an in-situ real-time observation system was constructed in this study with the assistance of computational fluid dynamics (CFD) simulation, and used to determine the transport and deposition behaviors of particle tracers on a corrugated microfiltration membrane surface (sawtooth shape, height ≈ 197 ± 14.7 μm, width ≈ 805.5 ± 44.5 μm). It was observed that most particles traveled wavily along the membrane surface pattern. Meanwhile, The particles entering the pattern valley were (i) trapped stagnantly at Ul = 0.05 m/s (Re = 228), while oscillated (ii) spirally in the direction of the pattern valley at Ul = 0.08 m/s (Re = 364), and (iii) irregularly at Ul = 0.1 m/s (Re = 445). During oscillation, some particles were able to escape the valley and return to the bulk flow. Complementary numerical simulation results indicated that the surface pattern induced local turbulence (wake) and boundary layer separation were the major mechanisms underlying the observed particle behaviors. These intriguing results gave rise to an intuitive understanding of the dynamics of particle transportation associated with patterned membrane filtration. Accordingly, a self-cleaning membrane may be prepared by optimizing the patterns as well as the superficial liquid velocities to invoke strong wake flow capable of mitigating particle deposition on membrane surfaces.