Scale Up of Polyamide Reverse Osmosis Membranes Surface Modification with Tethered Poly(Acrylic Acid) for Fabrication of Low-Fouling Spiral-Wound Elements

Scale up of atmospheric pressure plasma-induced graft polymerization (APPIGP) was demonstrated for surface nano-structuring (SNS) of a base polyamide (PA) reverse osmosis (RO) membrane with tethered poly(acrylic acid) (PAA) chains. Large SNS-PAA-PA membrane sheets, measuring 76.2 cm × 60.9 cm, were synthesized and used to fabricate small spiral-wound low fouling seawater RO elements (2.5 in. × 21 in.). The SNS-PAA-PA membrane sheets were of high spatial uniformity with respect to both water permeability and salt rejection. Lower SNS-PAA-PA membrane fouling propensity, relative to commercial membranes, was demonstrated in BSA and sodium alginate fouling tests of both membrane coupon and spiral-wound elements. Permeability recovery, upon water flushing of the fouled SNS-PAA-PA spiral-wound membrane elements was complete. Complete permeability recovery was also achieved for the sodium alginate fouled Dow SW30 element upon water flushing; however, permeability recovery was lower (91.6%) for the BSA fouled element, thus suggesting the need for added chemical cleaning. The study results suggest that APPIGP process scale up is feasible for fabrication of commercial-scale low fouling spiral-wound RO elements. However, further scale up toward continuous APPIGP will be required for larger size elements and automated element fabrication should be employed to minimize membrane and element construction imperfections.