(647f) Novel Amphiphilic Zwitterionic Copolymer Membranes of ~ 1nm Pore Size for Industrial Wastewater Treatment and Reuse

Membranes with ~1 nanometer effective pore size that allow removal of high oil/organic content (dyes, industrial chemicals, surfactants etc.) have numerous applications in the treatment of wastewater from textile plants, oil refineries, fracking and oil extraction. The small effective pore size of such membranes can potentially provide better effluent quality and prevent the environmental release of a wider range of pollutants. However, there are very few commercial membranes in this pore size range, and those that are available exhibit poor selectivity, charged surfaces which lead to complex separation mechanisms, and fouling due to the accumulation of feed components on the membrane surface. In addition to high flux, sharp selectivity and exceptional fouling resistance to common foulants in wastewaters, membranes for these applications should also have high chemical resistance and be easily fabricated into large-area membranes. Zwitterionic groups have been shown to strongly resist biomacromolecular fouling due to their high degree of hydration, which makes them promising for membrane applications. We have introduced a new class of membranes whose selective layers are made of self-assembling zwitterionic amphiphilic random copolymers. These membranes derive not only fouling resistance but also their permeability and selectivity from this self-assembled nanostructure. In this study, we evaluate the potential and performance of these new membrane materials in wastewater treatment. We synthesized random copolymers of a hydrophobic monomer (trifluoroethyl methacrylate) and two zwitterionic monomers (sulfobetaine methacrylate, phosphobetaine methacrylate) by free radical polymerization. These copolymers self-assemble into bicontinuous networks of ~1 nm nanochannels, driven by the strong electrostatic interactions between the zwitterionic groups, and documented by transmission electron microscopy (TEM). Membranes manufactured by coating these copolymers on commercially available support membranes exhibit size-based selectivity with a ~1 nm size cut-off demonstrated by filtering negatively charged dyes. We have studied how feed composition such as ionic strength and presence of foulants in varying wastewater streams affects membrane performance. Specifically, we have tested the performance of these membranes by filtering single foulants, and simulated wastewater feeds. These membranes are extremely resistant to fouling by proteins and oil emulsions, fully retaining their permeability even during the filtration of the foulant solution in dead-end mode for up to 7 days. They are also stable in a wide range of chemical solutions: salt solutions (upto 1M NaCl), acidic and basic buffers, as well as chlorine. They exhibit a sharp, size-based cut-off for organic molecules such as dyes found in textile wastewater. Their low salt rejection allows operation at lower pressures. These results indicate the promise of this new family of membrane materials for industrial wastewater treatment, reclamation and reuse.