Quantifying Charge Effects on Fouling Layer Strength and (Ir)Removability during Cross-Flow Microfiltration.

Mads Koustrup Jørgensen,Tuve Mattsson

doi:10.3390/membranes11010028

Mads Koustrup Jørgensen, Tuve Mattsson

Open Access

https://doi.org/10.3390/membranes11010028

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Abstract

Fouling of membranes is still an important limiting factor in the application of membrane technology. Therefore, there is still a need for an in-depth understanding of which parameters affect the (ir)removability of fouling layers, as well as the mechanisms behind fouling. In this study, fluid dynamic gauging (FDG) was used to investigate the influence of charge effects between negatively charged foulant particles and cations on cake cohesive strength. Fouling cakes’ thicknesses and cohesive strengths were estimated during membrane operations, where microfiltration (MF) membranes were fouled in a feed-and-bleed cross-flow filtration system with low and highly negatively charged polystyrene–polyacrylic acid core-shell particles. In addition, an added procedure to determine the irremovability of cakes using FDG was also proposed. Comparing layers formed in the presence and absence of calcium ions revealed that layers formed without calcium ions had significantly lower cohesive strength than layers formed in the presence of calcium ions, which is explained by the bridging effect between negatively charged particles and calcium ions. Results also confirmed more cohesive cakes formed by high negative charge particles in the presence of calcium compared to lower negative charge particles. Hence, it was demonstrated that FDG can be used to assess the cohesive strength ((ir)removability) of cake layers, and to study how cake cohesive strength depends on foulant surface charge and ionic composition of the solution.

Highlights

Membrane filtration is a flexible, compact, and energy-efficient technology widely used in applications ranging from the dairy industry [1,2,3] and breweries [4] to wastewater treatment [5] and water purification [6]
This study aimed to demonstrate this effect, and to show how fluid dynamic gauging (FDG) can be used to quantify the effect of chemical interactions on fouling layer cohesive strength for a system where bridging between particles is present
High surface charge (HC) particles were formed by adding HPC and PAA in 1:1 ratio, whereas low surface charge (LC) particles were synthesised by adding HPC and PAA at a 3:1 ratio

Summary

Introduction

Membrane filtration is a flexible, compact, and energy-efficient technology widely used in applications ranging from the dairy industry [1,2,3] and breweries [4] to wastewater treatment [5] and water purification [6]. Fouling leads to increased energy demand, chemical cleaning, membrane replacement, labour for process technicians, and thereby higher operational costs. To reduce these costs, fouling prevention is necessary, e.g., by pre-treatment (such as coagulation/flocculation) and operating at high shear stress near the surface to prevent deposition [8,9,10]. Fouling can be grouped into categories of removable, irremovable, and irrecoverable fouling [8]. Removable fouling can be removed by physical cleaning, whereas chemical cleaning may degrade and remove some of the irremovable fouling. The fouling that cannot be removed by chemical and physical cleaning is denoted irrecoverable fouling

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