Polyamide desalination membrane characterization and surface modification to enhance fouling resistance

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Title: Polyamide desalination membrane characterization and surface modification to enhance fouling resistance
Author: Van Wagner, Elizabeth Marie
Abstract: The market for polyamide desalination membranes is expected to continue to grow during the coming decades . Purification of alternative water sources will also be necessary to meet growing water demands . Purification of produced water , a byproduct of oil and gas production , is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs . However , current polyamide membranes are prone to fouling , which decreases water flux and shortens membrane lifetime . This research explored surface modification using poly (ethylene glycol ) diglycidyl ether (PEGDE ) to improve the fouling resistance of commercial polyamide membranes . Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies . Membrane performance was found to be sensitive to crossflow testing conditions . Concentration polarization and feed pH strongly influenced NaCl rejection , and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed . Two commercial polyamide membranes , including one reverse osmosis and one nanofiltration membrane , were modified by grafting PEGDE to their surfaces . Two different PEG molecular weights (200 and 1000 ) and treatment concentrations (1 % (w /w ) and 15 % (w /w ) ) were studied . Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram] /cm2 ) , although the largest changes were observed for low PEGDE graft densities . Surface properties including hydrophilicity , roughness and charge were minimally affected by surface modification . The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n -decane and a charged surfactant . Several PEGDE -modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux , possibly due to steric hindrance imparted by the PEG chains . Fouling resistance was higher for membranes modified with higher molecular weight PEG . Fouling was more extensive for feeds containing the cationic surfactant , potentially due to electrostatic attraction with the negatively charged membranes . However , fouling was also observed in the presence of the anionic surfactant , indicating hydrodynamic forces are also responsible for fouling .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1315
Date: 2011-01-31

Citation

Polyamide desalination membrane characterization and surface modification to enhance fouling resistance. Doctoral dissertation, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1315 .

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