Membranes used for desalination still face challenges during operation. One of these challenges is the buildup of salt ions at the membrane surface. This is known as concentration polarization, and it has a negative effect on membrane water permeance and salt rejection. In an attempt to decrease concentration polarization, a line-and-groove nanopattern was applied to a nanofiltration (NF) membrane. Aqueous sodium sulfate (Na2SO4) solutions were used to test the rejection and permeance of both pristine and patterned membranes. It was found that the nanopatterns did not reduce but increased the concentration polarization at the membrane surface. Based on these studies, different pattern shapes and sizes should be investigated to gain a fundamental understanding of the influence of pattern size and shape on concentration polarization.

This contribution describes a method to reduce bacteria fouling on ultrafiltration membranes by applying nanoscale line-and-groove patterns on the surface of membranes. Nanoimprint lithography was used to pattern the polysulfone membrane surfaces with a peak height of 66.2 nm and a period of 594.0 nm. Surface characterization using scanning electron microscopy and atomic force microscopy confirmed that patterning was successful over the entire stamped area of the membrane. Water permeance tests determined that the permeance decreased by 36% upon patterning. Static batch experiments that explored the attachment of Escherichia coli K12 cells to the membranes demonstrated that the patterned membranes had a 60% lower attachment of microbes than the nonpatterned membranes. Dynamic bacteria fouling experiments using E. coli cells showed that the patterned membranes had a higher flux recovery ratio (88%) compared to the nonpatterned membranes (70%). On the basis of these studies, we suggest that patterning membranes can reduce the initial attachments of microbial cells and that different pattern sizes and shapes should be investigated to gain a fundamental understanding of their influence on bacteria fouling.

Temperature swing solvent extraction (TSSE) utilizes an amine solvent with temperature-dependent water solubility to dissolve water at a lower temperature to concentrate or crystallize the brine and the phases are separated. Then, the water in solvent mixture is heated to reduce water solubility and cause phase separation between the solvent and water. The solvent and de-salted water phases are separated, and the regenerated solvent can be recycled. Issues with current TSSE solvents include the high solvent in water solubility and the high solvent volatility. This project used the highly tunable platform molecule imidazole to create two 1-butylimidazole isomers, specifically 1-propyl-4(5)-methylimidazole, to test their effectiveness for TSSE. The imidazoles take in more water than their current state-of-the-art counterparts, but do not desalinate the product water and dissolve in water at higher concentrations. Thus, while imidazoles make intriguing candidates for TSSE, further work is needed to understand how to design imidazoles that will be useful for TSSE applications.