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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ConFluReM (Controlling Fluid Resistances at Membranes)

Teaser

Summary

Synthetic membranes have changed todayâ€™s world in areas such as (i) water desalination and disinfection, (ii) medical treatment for open heart surgery and kidney support, (iii) chemical, gas and bioprocess engineering. These disruptive developments have only been able to emerge when multiple disciplines such as materials science, fluid mechanics, device design and process system developement were integrated. Unfortunately, todayâ€™s scientific membrane community focuses predominantly on the development of new materials aiming for superior transport properties inside the membrane: too little attention is paid to the molecular transport resistances outside the membrane material at the membrane-fluid interface. The potential of new membrane materials will remain ineffective as high and selective transport rates always go along with molecular transport resistances emerging at the membrane-fluid interface in the form of diffusion limitations in the laminar boundary layers. In order to make full use of the very many new materials, also new means to control and minimize such fluid based resistances need to be developed.

With respect to the prevailing challenge of fluid related resistances in membrane separation processes, the proposed research develops a rigorous methodology to control and improve mass transport through the membrane-fluid interface. Therefore â€œControlling Fluid Resistances at Membranesâ€ (ConFluReM) establishes strategic tools in fabrication, characterization and simulation to develope new instruments to:

i) comprehend and quantify the prevalent mass transport resistances in representative membrane separation processes,

ii) synthesize and fabricate nano-, micro- and mesoscale material systems as instruments to control and overcome the limitations of concentration polarization and fouling,

iii) ultimately control and overcome the negative influence of concentration polarization and concentration polarization induced fouling and scaling.

Work performed

The proposed research in â€œControlling Fluid Resistances at Membranesâ€ (ConFluReM) has successfully passed all milestones so far. Twelve papers addressing the various dimensions have been published describing means to control and minimize mass transport through the membrane-fluid interface. Thirteen national and international conferences have been visited by the ConFluReM-Team to present the recent publications. Two award winning presentations were given on fundamental and applied research.

Here, our research is outlined addressing new instruments to quantify, prevent, and overcome mass transport resistances at the membrane-fluid interface. ConFluReM goes dramatically beyond common measures: it aims to introduce turbulence and better mixing at the membrane surface while minimizing energy dissipation. This is achieved through designing, describing and optimizing the nano-scale membrane surface properties, the channel topology for fluid flow, and the initiation and continuous actuation of transient gradients in the fluid channels.

Here we demonstrate our approach on the design, description and development of sterile membrane filters that emerged recently to pretreat dialysate liquids fed to a hemodialysis filtration process. Their application significantly enhances the survival rate during dialysis treatment. However, little is known about the fluid-flow coupled mass transport in such single use membrane modules. We report a detailed analysis of the local three-dimensional flow-field and its effects on i) the local permeate flux distribution identifying the active membrane area, ii) the time-dependent silica particle deposition during membrane filtration and iii) the effect of drag force on the silica particle deposition onto the membrane. These detailed insights encourage the use of our new strategic flow imaging competences when designing new membrane module configurations.

Final results

ConFluReMâ€™s novelty stems from the many new developments that have emerged over the past five years in the disciplines of nanofabrication, additive manufacturing and micro- and mesofluidics. Using these strategic competences we describe the microscopic local reality when colloidal particles aggregate at membrane pores or inside more complex porous media. Optical methods in combination with microfluidic control supported by computational fluid dynamic simulations enable a rigorous description of polarization and fouling phenomena. The sophisticated interplay of these competences will guarantee a new dimension in the exploration of the central question of ConFluReM â€œhow we can succeed to minimize the fluid resistance at the membraneâ€ so that new membrane materials emerging in other membrane science fields can operate and develop their full potential.