Airfoil-shaped filament feed spacer for improved filtration performance in water treatment

Published on by in Academic

Airfoil-shaped filament feed spacer for improved filtration performance in water treatment

Abstract

Optimal spacer design enhances the filtration performance in spiral-wound modules by controlling the local hydrodynamics inside the filtration channel. A novel airfoil feed spacer design fabricated using 3D-printing technology is proposed in this study. The design is a ladder-shaped configuration with primary airfoil-shaped filaments facing the incoming feed flow. The airfoil filaments are reinforced by cylindrical pillars supporting the membrane surface. Laterally, all the airfoil filaments are connected by thin cylindrical filaments. The performances of the novel airfoil spacers are evaluated at Angle of Attack (AOA) of 10° (A-10 spacer) and 30° (A-30 spacer) and compared with commercial (COM) spacer. At fixed operating conditions, simulations indicate steady-state hydrodynamics inside the channel for A-10 spacer, while an unsteady state is found for A-30 spacer. Numerical wall shear stress for airfoil spacers is uniformly distributed and has a higher magnitude than the COM spacer. A-30 spacer design is the most efficient in ultrafiltration process with enhanced permeate flux (228%) and reduced specific energy consumption (23%) and biofouling development (74%) as characterized by Optical Coherence Tomography. Results systematically demonstrate the influential role of airfoil-shaped filaments for feed spacer design. Modifying AOA allows localized hydrodynamics to be effectively controlled according to the filtration type and operating conditions.

Introduction

Over the past decade, the freshwater shortage has been continuously rising and putting tremendous pressure on existing freshwater resources1. In addition, the recent spreading of coronavirus pandemic, with the ability to infect water for days to weeks2, places tremendous stress on producing safe drinking water. Membrane filtration technologies such as reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have gained attention due to their potential to yield a high quantity and safe drinking water with reasonable operating costs3. However, the accumulation of (bio)fouling on the membrane surface ruins filtration performance and deteriorates water quality4. Therefore, controlling the (bio)fouling growth is essential for greater water productivity while minimizing energy consumption. The prevention of bacterial growth by smartly designing filtration module components constitutes a straightforward and eco-friendly approach. Focusing on designing an optimal feed spacer in spiral-wound modules (SWM) has recently gained significant thrust to enhance water productivity, reduce (bio)fouling growth, and lower energy consumption5,6.

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