(678a) RO Membranes with Surface Tethered Poly(acrylic acid) Chains for Low Fouling, Ease of Cleaning, Selective Removal and Hydraulic Permeability and Salt Rejection Tunability

Surface nano-structuring of reverse osmosis (RO) membranes has advanced in recent years demonstrating the potential application of polymeric layers tethered onto on base polyamide (PA) thin-film composite (TFC) membranes. Such layers can serve to repair imperfections in the base RO membrane, reduce fouling and mineral scaling propensity, improve cleaning efficacy, and even allow one to overcome the typical permeability-selectivity tradeoff. Increased rejection of certain solutes has also been reported. The ability of tethered layer to provide the above beneficial improvements in membrane performance and responsiveness to environmental conditions (e.g., pH, temperature and salinity) is governed by both the chemistry of the tethered polymer chains, as well as the surface number density and length of these chains. In the present work, based on compilation of multiple experiments, it is shown that tethering of stimuli-responsive poly(acrylic acid) (PAA) chains onto a PA-TCF base membrane, with a target permeability and salt rejection, can be accomplished via PA surface activation via atmospheric pressure plasma, followed by graft polymerization to attain a high density brush layer. The resulting surface nano-structured (SNA) membranes, depending on the starting properties of the base RO membranes, can achieve highly tunable performance, and have remarkable low fouling/scaling propensity, and can be easily cleaned with low salinity water. Such membranes can also improve the rejection of difficult to remove nitrate and boron. Moreover, scale-up of the above approach is feasible and can be used to prepare highly uniform (with respect to separation performance) large surface area membrane sheets that were then utilized to fabricate small spiral-wound element. The above approach will be reviewed, and performance data, based on laboratory tests with both small membrane coupon and spiral-wound membrane elements, will be presented along with technoeconomic analysis of the competitive cost of the SNS-PAA-PA membrane fabrication.