Fouling mitigation in tubular membranes by 3D-printed turbulence promoters

Sarah Armbruster,Oskar Cheong,Jonas Lölsberg,Svetlana Popovic,Süleyman Yüce,Matthias Wessling

doi:10.1016/j.memsci.2018.02.015

Abstract

Despite intensive research, fouling remains a severe problem in membrane filtration. It is often controlled by applying turbulent flow which requires a higher energy consumption. So-called turbulence promoters or static mixers can be inserted into the flow channel of tubular membranes. They deflect the fluid, induce vortices, enhance particle back-transport and increase the shear rate at the membrane surface, thus mitigating fouling. However, little is known how the geometry of such turbulence promotors affects the reduction of fouling. We investigate how different 3D-printed mixer geometries affect fouling and improve the flux during filtration with humic acid. Most mixer geometries used in the present study are based on a twisted tape; a Kenics static mixer is investigated as well. Static mixers with changing diameter prove to be less effective than twisted tape mixers with constant diameter which lead to an increase in permeate flux of around 130%. The highest flux improvement of 140% can be reached by applying a Kenics mixer. Regardless of their geometry, all investigated static mixer cause higher permeate fluxes at same specific energy consumption. Again, the Kenics mixer proves to be the most efficient static mixer. The presented mixer geometries can be fabricated with undercut injection molding techniques and represent a simple and viable option to make tubular membrane based filtration processes more efficient.

Highlights

Membrane filtration has long been used in a broad variety of industries ranging from the food and beverages industry to water treatment for all kinds ofwater to purifying highly valuable product streams in biotechnology
Static mixers with changing diameter prove to be less effective than twisted tape mixers with constant diameter which lead to an increase in permeate flux of around 130 %
In comparison to the system without mixer where a flux of 105 LM H is reached at a transmembrane pressure (TMP) of 1.3 bar, the systems with a twisted tape static mixer achieve fluxes as high as 240 LM H at the same TMP

Summary

Introduction

Membrane filtration has long been used in a broad variety of industries ranging from the food and beverages industry to water treatment for all kinds of (waste)water to purifying highly valuable product streams in biotechnology. In contrast to other separation technologies, membrane filtration does not require large amounts of energy. This is one of the major benefits of membrane processes and makes them a sustainable, energy- and cost-efficient alternative to traditional thermal separation processes. Concentration polarization and fouling remain challenges in membrane filtration. Once fouling has occurred and the membrane’s filtration capacity has declined, the membrane has to be cleaned or even replaced. Cleaning is costly as chemicals might be needed, and the filtration is interrupted. The main focus has to be put on mitigating fouling to avoid cleaning interruptions of filtration processes that would weaken the economic viability of membrane processes

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Conclusion