Fouling-resistant membranes for the treatment of flowback water from hydraulic shale fracturing: A pilot study

Polyacrylonitrile hollow fiber ultrafiltration (UF) and polyamide spiral wound reverse osmosis (RO) membrane modules were surface-modified by contact with an aqueous solution containing dopamine to deposit polydopamine on the membrane surfaces and other wetted parts inside the modules. UF modules were further modified by grafting poly(ethylene glycol) (PEG) brushes to the polydopamine coating. Polydopamine and polydopamine-g-PEG coatings increase hydrophilicity of the membrane surfaces and have previously been shown to improve fouling resistance towards model oil/water emulsions in laboratory studies. In a pilot-scale test treating hydraulic fracturing flowback water from the Barnett Shale region of Texas, the fouling performance of modified UF and RO membrane modules was compared to that of unmodified analogs. UF modules were used to remove most of the highly fouling organic matter in the feed before desalination by a train of RO elements. Polydopamine-modified UF modules maintained higher flux, lower transmembrane pressure difference, and improved cleaning efficiency relative to unmodified modules. The polydopamine coating did not appear to improve RO fouling behavior, presumably because most of the organic foulants had been removed by UF pretreatment of the feedwater. However, higher and more stable salt rejection was observed in modified RO modules than in unmodified modules.