This research focuses on the design of small protrusions (micromixers) fabricated on reverse-osmosis membranes with the objective of reducing biofouling by increasing the amount of turbulent mixing along the membrane surface. Micromixers have been experimentally and computationally shown to induce chaotic mixing and increase shear stress on the membrane surface.

Problem Membrane-based separation processes, such as reverse osmosis (RO) and ultra- or nano-filtration, are commonly used in industrial applications such as desalination, waste-water treatment, and power generation. Major problems associated with membrane-based separation processes include fouling and high pressure loss, which decrease the efficiency of the filtration, decrease membrane lifetime, and increase operation costs.

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Computational Approach

Computational fluid dynamics models were developed to simulate flow patterns and mass transfer in the feed channel with membranes consisting of different patterns of micromixers.

3D mesh of membrane with micromixers

A design analysis was performed to optimize the shape of micromixers to maximize scouring on the membrane surface.
The total simulated mass transfer of a tracer from the surface of the membrane was used as a metric to compare the scouring effectiveness among the various micromixer patterns. The parameterization results indicate that the greatest scouring occurs when the chevron angle and chevron protrusion depth are maximized, while the chevron pattern wavelength and spacing between chevrons are minimized.	Deeper chevron protrusions induce a larger flow acceleration toward the membrane surface

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Experimental Approach

Epoxy micromixers were printed directly onto membrane surfaces, and different patterns were evaluated experimentally. Fluorescence hyperspectral imaging results showed that regions of simulated high shear stress on the membrane corresponded to regions of lower bacterial growth in the experiments, while regions of simulated low shear stress corresponded to regions of higher bacterial growth.		Membrane printed with micromixers
The top image is the relative microbial concentration as observed by hyperspectral imaging; the bottom image is the simulated relative shear stress on the membrane surface.

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Publications

• Altman, S. J., H. D. T. Jones, L. K. McGrath, D. M. Haaland, M. B. Sinclair, 2007, Testing of RO Membrane Biofouling Using Fluorescent Hyperspectral Imaging, 2007 North American Membrane Society Conference, May 12-16, 2007, Orlando, FL. [SAND2007-3234C]
  
  
• Clem, P.G., “Smart Materials for Integrated Microsystems,” 10th Germany-American Frontiers of Engineering Symposium, National Academy of Engineering and Alexander von Humboldt Society, Hamburg, Germany, April 25-28, 2007.
  
  
• Cornelius, C. J., C. H. Fujimoto, L. He, D. Perahia, Interfacial Characteristics of a Potentially Anti-biofouling Highly Rigid Ionomer, 2007 APS March Meeting, Session X17: Structure and Dynamics of Polymer Films.
  
  
• He, L., E. B. Watkins, J. Majewski, C. H. Fujimoto, C. J. Cornelius, D. Perahia, Water Diffusion in Ultrathin Ionomer Thin Films: Neutron Reflectivity Study, 2007 APS March Meeting, Session A17: Charged and Ion - Containing Polymers.
  
  
• Hibbs, M., C. J. Cornelius, 2007, Synthesis and Characterization of Novel Ionomer Membranes for Water Treatment Applications, 2007 North American Membrane Society Conference, May 12-16, 2007, Orlando, FL. [SAND2007-2432C]
  
  
• Ho, C.K., S.J. Altman, H.D.T. Jones, S.S. Khalsa, L.K. McGrath, and P.G. Clem, 2008, (in press), Analysis of Micromixers to Reduce Biofouling in Reverse-Osmosis Membranes, Accepted for publication in the "Desalination - Outstanding Papers from NAMS 2007" special issue of Environmental Progress. [SAND 2008-1239J]
  
  
• Ho, C.K., S.S. Khalsa, P. Clem, M. Niehaus, S. Brown, and W. Hart, 2007, Analysis of Micro-Mixers to Reduce Fouling on Membrane Surfaces, 2007 North American Membrane Society Conference, May 12-16, 2007, Orlando, FL. [SAND2007-3022P]
  
  
• Jones, H. D. T., S. J. Altman, C. K. Ho, L. K. McGrath, P. G. Clem, D. M. Haaland, M. B. Sinclair, and D. K. Melgaard, 2007, Hyperspectral Fluorescence Imaging of Biological Samples, Pittsburgh Conference, February 25 - March 1, 2007, Chicago, IL. [SAND2007-1155C]
  
  
• Khalsa, S.S. and C.K. Ho, 2008, Design Optimization of Anti-Fouling Micromixers for Reverse Osmosis Membranes, Abstract accepted for the 23rd Annual WateReuse Symposium, Dallas, TX, September 7-10, 2008.
  
  
• Webb, S. W., 2007, High-Fidelity Simulation of Fluid Flow and Species Behavior in RO Membranes, 2007 North American Membrane Society Conference, May 12-16, 2007, Orlando, FL. [SAND2007-2311A]