An Integrated approach for characterization of polyamide reverse osmosis membrane degradation due to exposure to free chlorine

Reverse osmosis (RO) polyamide (PA) membrane integrity loss, performance degradation, and alteration of surface properties due to exposure to chlorine were evaluated experimentally via a fluorescent marker (uranine) based method, water permeability and salt flux measurements, and surface characterization via XPS, AFM and contact angle measurements. Membrane exposure to chlorine (4-200 mg/L NaOCl solutions) revealed that although membrane surface roughness increased with chlorine exposure intensity (ppm-h), surface hydrophilicity increased as inferred by the decline (up to 5.2-9.6%) of the surface energy of hydration. Comparative analysis of marker transport for membranes that have undergone chlorine exposure of 125-2000 ppm-h demonstrated that the membrane marker permeability coefficient (B) increased by up to a factor of ~5 relative to the intact membrane. While the severity of membrane integrity loss/performance degradation correlated to a reasonable degree with ppm-h of chlorine exposure, the severity of membrane integrity loss, at the same chlorine ppm-h, was greater for higher exposure concentration. Membrane integrity loss, over the same exposure levels, was quantified by an equivalent cylindrical breach that was in the range of about 14-40 µm, increasing in size with the intensity of chlorine exposure.