This NSF award by the Chemical and Biological Separations program supports work by Professors Jeffrey McCutcheon and Benny Freeman to develop a new method for chemically modifying commercial reverse osmosis membranes for use in forward osmosis and pressure retarded osmosis applications. Forward osmosis (FO) and pressure retarded osmosis (PRO) are sibling technologies that fall under the broader distinction of engineered osmosis (EO). This platform relies on osmotic flow induced by concentration differences across a membrane to purify water, dewater solutions and generate electricity. FO has recently been considered for seawater desalination, wastewater reuse, and food processing and is considered a low cost alternative to reverse osmosis (RO) and evaporative approaches. PRO has been considered for harvesting osmotic potential at river deltas and within "osmotic engine" systems to generate electricity with a hydroturbine. Any EO technology requires a tailored membrane that not only is highly selective, but also exhibits properties that promote osmotic flow. Today's commercial desalting membranes are designed specifically for reverse osmosis. These membranes exhibit excellent selectivity and permeability, but also employ thick porous support layers. These layers provide little resistance to hydraulic flow in RO. However, they dramatically impact mass transfer in forward osmosis, causing what is commonly referred to as internal concentration polarization. Early work has shown that RO membranes have very poor flux performance when evaluated in FO or PRO. A significant amount of this resistance is caused by poor wetting of the support layers, which are comprised of hydrophobic polymers. This work will demonstrate that a chemical modification of reverse osmosis membrane support layers with polydopamine and its analogs will enhance osmotic flux by increasing the hydrophilicity of the support layers. Once hydrophilized, the layers will saturate, thereby providing the necessary continuity of the water phase to reduce mass transfer resistances. Early work has already shown that in some cases, water flux can be increased by a factor of 10 or more when compared to an unmodified membrane. This solution may provide an alternative to building new membranes using techniques that may be difficult to scale or will require years of development to achieve similar performance to today's RO membranes.
In a world of ever increasing demand for scarce water and energy resources, new technology platforms, like EO, offer new possibilities. Desalination and power production using EO will be enabled through the development of new, tailored membranes. However, if we are able to use existing membrane technology with a simple modification, we do not need to develop an entirely new membrane platform. In fact, the proposed modification method is scalable and therefore easily implemented into existing membrane productions lines. Membrane manufacturers are more likely to implement changes to their production scheme if it doesn't require rebuilding their entire manufacturing infrastructure. Furthermore, this investigation will represent the first time that modification of a RO membrane support layer has been considered to increase flux performance.
To achieve our goals, a better understanding of how the coating occurs within a porous material (the RO membrane support layer) will be necessary. The University of Connecticut will evaluate the coating procedure to maximize performance improvements while the University of Texas will develop analog chemistries to polydopamine that may be more appropriate for deposition within a porous structure. Ultimately, we will develop an understanding of how chemistry and modification technique impact osmotic flux performance across modified RO membranes.
According to the National Academy of Engineering, one of the Grand Challenges for Engineering is providing access to clean water for mankind. The development of emerging water treatment technologies like forward osmosis could reinvigorate interest in desalination and wastewater reuse due to its promised benefits of low cost. As such, both PIs will use this work to stimulate interest in water within their educational and outreach programs. At the University of Texas, Professor Freeman will provide research opportunities for high school students and teachers, giving invaluable experience to help promote engineering education in Texas high schools. At the University of Connecticut, Professor McCutcheon will be an active participant in Universitas 21, an organization that promotes undergraduate research across disciplines and oceans. Twenty three member universities provide programming for undergraduates to present their research, and UCONN is one of two American university participants. Professor McCutcheon will help develop programming for a summer school to be held at UCONN as well as mentor the UCONN undergraduates who plan on attending the annual conference and other meetings. The PIs will collaborate in establishing an REU exchange program, called UCONNect2Texas, which will involve undergraduate students from each school visiting the other for a period of 10 weeks during the summer.
