Membrane filtration performance enhancement and biofouling mitigation using symmetric spacers with helical filaments

Abstract

Optimization of the feed spacer geometry is one of the key challenges for improved ultrafiltration performance in water treatment and desalination. Novel feed spacers with different number of helices (1-3) along the spacer filament are proposed. To elucidate the intrinsic ability of the helical feature on filtration process improvement, experiments were conducted at two different fluid inlet velocities (U0 = 0.166 m/s and 0.182 m/s). The presence of micro-helices in the filaments aids significantly in increasing the specific permeate flux when compared to the standard spacer (without helices). The highest improvement was observed in the case of 3-helical spacer (291% specific permeate flux increase at U0 = 0.182 m/s). Furthermore, Optical Coherence Tomography OCT) imaging demonstrated less (bio)fouling amount developed on membrane surface equipped with helical spacers, whereas, a thicker and more dense cake fouling layer appeared in the case of standard spacer. Moreover, novel helical design spacers reduce the pressure drop inside the channel. The 3-helical spacer was found to have the least feed-channel pressure drop (65% of decrease relative to standard spacer). Numerical analysis was simultaneously realized by the Direct Numerical Simulation (DNS) technique to understand the hydrodynamic behavior at an elemental level inside the filtration channel. Low shear stress and high local velocity magnitudes were observed in presence of helical spacers resulting in (bio)fouling mitigation on filtration membrane surface.