Water Treatment Applications with Integrated Charged NF and Iron Nanoparticle Functionalized Membranes

Nanofiltration (NF) membranes play an important role where selective separations (in contrast to RO) or partial desalinations are needed. NF membranes are used in energy industries and in various water treatment (including virus separations) applications. In various energy area applications it is important to have membranes where one can obtain selective separations of divalent cations (such as, Ca and Mg) from high salt solutions. This allows reduction of osmotic pressure effects and also for reuse of permeate water. On the other hand, functionalization of microfiltration membranes with LbL assembly or metal nanoparticles allows applications where reactive medium may be needed. This presentation will focus on energy related, and groundwater treatment applications. Depending on the types of applications (such as in coal-fired power plant scrubber water reuse) selective partial desalination of mixed salts by NF membranes and trace toxic metal capture (such as, Se) by functionalized MF membranes could be a potential treatment scheme. The special features for membrane processes that make them attractive for industrial applications are their compactness, ease of fabrication, operation, and modular design. We have made highly significant advancements in establishing the effectiveness of nanofiltration membrane systems in terms of salt separation selectivity, and the role of various levels of TDS on water flux and rejection behavior with module systems for low hign water recovery areas. Two types (positively-charged, and negatively-charged) of modules were evaluated. Even at 10 bar applied pressure, water flux as high as 58 LMH (34 gal/ft² day) at 25 oC can be obtained. The increase of temperature of feed water to 42 oC showed about 40% increase in water flux (as expected, due to viscosity effect) and insignificant loss of rejection of TDS. Since the water often contains trace toxic metals (such as selenate), pretreatment with functionalized membranes containing iron nanoparticles provides a new approach. Preliminary results starting with 2 ppm Se showed concentration < 5 ppb Se can be achieved with Fe NPs by reduction. The presentation will include: (1) membrane selection approaches, (2) NF results on selectivity and partial desalination, and high water recovery, (3) full-scale PAA functionalization of PVDF membranes and responsive flux behavior, (4) toxic metal and organic removal results. This research has been supported by Southern Company, and by NIH-NIEHS-SRP. Special thanks go to ULTURA Company, Oceanside, CA, for joint collaborative work in developing advanced NF membranes and full-scale functionalized membranes.