Produced water (PW) from energy-related activities is one of the most-significant wastewater streams in the United States and represents an exciting opportunity for water reuse. With this, PW contains high salt content and a wide variety of inorganic and organic contaminants, making treatment difficult and energy-intensive. Membrane technologies, including nanofiltration (NF) and reverse osmosis (RO), are the most commonly used treatment approaches for PW, but primarily due to membrane fouling, single membrane processes are not capable of treating highly impaired PW in an energy-efficient manner. Therefore, a pretreatment for NF/RO to reduce fouling is necessary for future membrane design. One innovative pretreatment scheme is the separation of charged components using electrodialysis (ED) prior to NF/RO. ED can remove most ions while achieving minimal removal of organic constituents due to the slow diffusivity of these macromolecules. In the integrated process, the diluate from the ED system, containing few inorganic ions but an organic composition nearly identical to the influent water, is treated with NF/RO. In turn, the NF/RO membranes experience substantially less fouling, leading to decreased energy costs and extended membrane lifetimes. The application of ED-NF/RO membranes has not been studied for PW, and a thorough understanding of membrane fouling by PW is missing. Thus, the objective of this study is to provide a systematic understanding of the ED, NF/RO, and ED-NF/RO processes with model PW containing organic acids (phthalic acid), proteins (BSA), and polysaccharides (alignate), and inorganic components (Na+, Cl-, SO42-, Ba2+, Ca+2, Mg+2). Operational characteristics of the membrane processes are monitored, and NF/RO membranes are autopsied following experiments to characterize fouling. Membrane characteristics and the buildup of organic and inorganic contents on the membrane surfaces are examined using surface techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR). Results with natural organic matter show that organic composition (i.e., hydrophobicity/hydrophilicity) significantly impact fouling properties and must be considered in system design, and that this hybrid system exhibits considerable promise for future PW reuse.

Electrodialysis pretreatment to reduce fouling of nanofiltration membranes for treatment of produced water

2019 Spring National Meeting

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