Abstract

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Three spacer designs, namely a non-woven commercial spacer (varying filament cross-section), a symmetric pillar spacer, and a novel hole-pillar spacer (constant filament diameter) were studied using Direct Numerical Simulations (DNS), 3-D printed and subsequently experimentally tested in a lab-scale ultrafiltration set-up with high biofouling potential feed water at various feed pressures. Independent of the applied pressure, the novel hole-pillar spacer showed initially the lowest feed channel pressure drop, the lowest shear stress, and the highest permeate flux compared to the commercial and pillar spacers. Furthermore, less biofilm thickness development on membrane surface was visualized by Optical Coherent Tomography (OCT) imaging for the proposed hole-pillar spacer. At higher feed pressure, a thicker biofilm developed on membrane surface for all spacer designs explaining the stronger decrease in permeate flux at high pressure. The findings systematically demonstrated the role of various spacer designs and applied pressure on the performance of pre-treatment process, while identifying specific shear stress distribution guidelines for engineering a new spacer design in different filtration techniques.

Highlights

  • Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance

  • Feed spacer is one of the critical components of the spiral wound membrane modules, which effectively influences the overall filtration ­performance[1,2]. It has a pivotal role in ensuring the mechanical support to the membrane surface and help the fluid flow between the membrane sheets while aiding in minimizing the concentration polarization/(bio)fouling by promoting fluid u­ nsteadiness[2,3,4] inside the filtration c­ hannel[5,6]

  • Research efforts were focused on modestly modifying the geometric parameters of commercial spacer such as spacer thickness, filament diameter, mesh size, internal filament angle, and spacer orientation to amend the hydrodynamics conditions within the feed ­channel[8,13,14,15,16,17,18,19]

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Summary

Introduction

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Feed spacer is one of the critical components of the spiral wound membrane modules, which effectively influences the overall filtration ­performance[1,2] It has a pivotal role in ensuring the mechanical support to the membrane surface and help the fluid flow between the membrane sheets while aiding in minimizing the concentration polarization/(bio)fouling by promoting fluid u­ nsteadiness[2,3,4] inside the filtration c­ hannel[5,6]. More complex spacer designs like honeycomb-shaped s­ pacer[31], triply periodic minimal surfaces (TMPS)[26], vibrating ­spacers[27], turbo-spacer using rotating ­turbines[32], and helical-type ­spacers[4] have shown promise in reverse osmosis (RO) and ultrafiltration (UF) processes These proposed novel spacer designs indicate favorable progress for enhanced filtration membranes, several constraints are still encountered and hamper their commercialization and industrial implementation. It includes the design c­ omplexity[26,32], the handling ­difficulty[27,32], the risk of membrane deformation/damage[24,25,33], and the high energy ­requirements[22,25,28]

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