Analysis of micromixers to reduce biofouling on reverse-osmosis membranes

Features (micromixers) that promote chaotic mixing were fabricated on reverse-osmosis 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 scouting and mixing in configurations with and without micromixers. Epoxy micromixers were printed directly onto membrane surfiaces, 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. In addition, the presence of the micromixers appeared to reduce the overall biofouling concentration in one series of experiments, but the results were inconclusive in another series of experiments. These results indicate that while the enhancement of mixing and shear stress via micromixers may delay or mitigate the onset of localized membrane fouling from biofilms or other contaminants, the impact of micromixers on the overall performance of reverse-osmosis membranes needs further investigation. (C) 2008 American Institute of Chemical Engineers Environ Prog.