IN SITU MODIFICATION OF DESALINATION MEMBRANES FOR IMPROVED PERFORMANCE
Nanofiltration and reverse osmosis are widely used today for desalination and water treatment. However, relative hydrophobicity of the top polyamide membrane layer, leads to high affinity toward small uncharged solutes and hydrophobic foulants. Additional drawback is the non-uniformity of polyamide, in which non-selective spots reduce overall selectivity.
Based on promising results obtained previously in our group,1,2 this study systematically examines improvement of polyamide membranes performance by surface grafting using concentration polarization-enhanced redox graft polymerization. In this way the selectivity of the grafted layer can be tuned towards model pollutants through the use of optimal monomers along with sealing the more permeable areas inherently present in the original active layer.
Main focus was on the monomer glycidyl methacrylate (GMA) for improving selectivity of uncharged solutes such as boric acid and representative endocrine-disrupting contaminants (EDCs). In combination with 3-(Methacryloylamino) propyl/ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide (SPP/SPE), a zwitterionic monomer, for improving fouling resistance.
Results from dead end experiments showed that GMA and SPP combination achieved enhancement in the rejection of EDCs model compounds (up to 50-60%, improvement) as well as boric acid (up to 35% improvement), with a moderate loss of flux. Accelerated fouling tests in cross flow cells resulted in unchanged salt rejection, enhanced boric acid rejection and fouling resistance of the modified membranes. Up-scaling optimal modification procedure to commercial RO modules is currently underway, in order to assess the full potential for improving, tuning and/or restoring modified membranes in real feed conditions.
1Bernstein, R., Belfer, S., & Freger, V. (2012). Journal of Membrane Science, 405, 79-84.
2Ben-David, A., Bernstein, R., Oren, Y., Belfer, S., Dosoretz, C., & Freger, V. (2010). Journal of Membrane Science, 357(1), 152-159.
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