Analysis of micromixers and biocidal coatings on water-treatment membranes to minimize biofouling.

Abstract

Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes negatively impacts in desalination and water treatment. With biofouling there is a decrease in permeate production, degradation of permeate water quality, and an increase in energy expenditure due to increased cross-flow pressure needed. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The overall goal of the work described in this report was to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers -UV-curable epoxy traces printed on the surface of a watertreatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated. Creation of low-cost, efficient water-treatment membranes helps assure the availability of fresh water for human use, a growing need in both the U. S. and the world. 3 EXECUTIVE SUMMARYSection 1: Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes has a negative economic impact in desalination and water treatment. With biofouling there is a decrease in permeate production and an increase in energy expenditure due to increased cross-flow pressure needed. Biofouling leads to increased cleaning expenditures, it accelerates the degradation of the membranes, and degrades the water quality of the permeate. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The goal of this project is to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers -UV-curable epoxy traces printed on the surface of a watertreatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated.Section 2: Features (micromixers) that promote chaotic mixing were fabricated on reverseosmosis membrane surfaces and evaluated using computational models and laboratory experiments to determine their effectiveness in reducing biofouling. Computational fluid dynamics models of membrane feed channels were developed using different patterns of micromixers on the membrane surface. The shear-stress distribution along the membrane surface was simulated for steady flows along the different micromixer configurations. In addition, the hypothetical mass transfer of a tracer from the membrane surface was used as a metric to compare the amount of scouring and mixing in configurations with and without micromixers. 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 co...