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Effects of water chemistry on NF/RO membrane structure and performance

  • Author(s): Mo, Yibing
  • Advisor(s): Hoek, Eric M.V.
  • et al.
Abstract

In recent decades, there has been increasing concern about water contaminated by chemicals of emerging concern (CECs), a.k.a., trace organic micropollutants or emerging contaminants. Recent advances in analytical procedures enable detection of compounds like pharmaceuticals & personal care products (PhPCPs), hormones, endocrine disrupting compounds (EDCs), disinfection by-products (DBPs) and synthetic organic chemicals (SOCs). Many members of these compound classes are carcinogen or mutagens. A number of conventional and advanced methods have been evaluated (individually and in combination) for removal of CECs from water sources, including enhanced coagulation, activated carbon, activated sludge, membrane bioreactors, riverbank filtration, nanofiltration (NF), reverse osmosis (RO), and advanced oxidation processes. NF and RO membranes can achieve very high removals of many CECs; however, removal of a specific solute by a given membrane can vary widely at different water treatment plants. It has been proposed that different membrane performances were due to variations in water chemistry (i.e., pH, TDS, hardness, etc.), but it was not specified as to why the water chemistry so profoundly influences observed CEC removal. This study attempts to relate how water chemistry affects NF and RO membrane performance by elucidating structural changes in the membrane barrier layer solely due to background water chemistry - using model membranes, and well controlled laboratory studies using different solutes and electrolytes. A recently proposed NF/RO structure-performance model used to fit experimental data suggests that NF/RO membranes become looser (i.e, lower rejection of trace organics and high water permeability) with increasing water ionic strength, pH and divalent content.

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