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    Unraveling pH Effects on Ultrafiltration Membrane Fouling by Extracellular Polymeric Substances: Adsorption and Conformation Analyzed with Localized Surface Plasmon Resonance

    Journal: Environ. Sci. Technol., Volume 56, OCT 18, page 14763–14773

    Authors: Ran, Noya; Sharon-Gojman, Revital; Larsson, Sara; Gillor, Osnat; Mauter, Meagan S.; Herzberg, Moshe

    Organizations: Israel Governmental Authority for Water and Sewage; [4501683711]

    Keywords: localized surface Plasmon resonance (LSPR); QCM-D; extracellular polymeric substances (EPS); ultrafiltration membranes; fouling; biofouling

    Extracellular polymeric substances (EPSs) can conform and orient on the surface according to the applied aquatic conditions. While pH elevation usually removes EPSs from membranes, small changes in pH can change the adsorbed EPS conformation and orientation, resulting in a decrease in membrane permeability. Accordingly, EPS layers were tested with localized surface plasmon resonance (LSPR) sensing and quartz crystal microbalance with dissipation monitoring (QCM-D) using a hybrid sensor. A novel membrane-mimetic hybrid QCM-D-LSPR sensor was designed to indicate both dry mass and mechanical load (wet mass) of the adsorbed EPS. The effect of pH on the EPS layer's viscoelastic properties and hydrated thickness analyzed by QCM-D corroborates with the shift in EPS areal concentration, Gamma S, and the associated EPS conformation, analyzed by LSPR. As pH elevates, the processes of (i) elevation in EPS layer's thickness (QCM-D) and (ii) decrease in the EPS areal density, Gamma S (LSPR), provide a clear indication for changes in EPS conformation, which decrease the effective ultrafiltration (UF) membrane pore diameter. This decrease in the pore diameter together with the increase in surface hydrophobicity elevates UF membrane hydraulic resistance.
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