(698d) pH-Responsive Membranes for Treatment of Wastewaters

Increasing environmental awareness and raw material prices have lead to increased exploration of nonconventional alternative energy sources. Specifically, coal bed methane and oil shale have been pursued as a means of fuel oil production; however, these sources of energy often lead to the production of large amounts of co-produced water which contains dissolved solids and oils. This waste water could serve as a potential solution to increasing water demands in industrialized nations, particularly arid regions such as the western United States, but the composition of these produced waters makes traditional treatment methods difficult and expensive. Membrane filtration has been proposed as an alternative to these traditional methods, but thus far has had limited success because of rapid membrane fouling.

Commercially available nanofiltration membranes have shown promise for converting these waste waters into water for beneficial uses if fouling could be minimized. We have modified nanofiltration membranes by growing pH responsive brushes from the membrane surface. Acrylic acid nanobrushes were grown from the surface of the membrane using UV-initiated polymerization. These nanobrushes swell or contract based on the pH of the feed stream. This occurs when the feed pH is above or below the isoelectric point of acrylic acid (pKa = 4.25), respectively. The state of the nanobrushes will affect the filtration properties of the membrane leading to improved performance.

Membrane performance has been characterized by comparison of membrane flux at various pH values as well as spectroscopy studies. The membranes showed improved fractionation abilities for assorted buffers and sugar solutions. Additionally, multiple wastewater streams from oil wells in northern Colorado and southern Wyoming were treated with the modified membranes.