Electrically Conducting Membranes - Challenges and Opportunities

Humans have been expending energy to clean water for millennia. While boiling water to kill pathogens or collect and use vapor are viable methods to produce potable water, water's large heat capacity makes this process energetically expensive, and economically unfeasible on a large scale. Membrane-based separation methods have emerged as the preferred water treatment technology, as membrane processes consume significantly less energy to produce water. However, membranes are prone to fouling, a fact that increases the cost of water and leads to significant operational complexity. We have developed a range of electrically conducting carbon nanotube - polymer composite membranes suitable for a range of water treatment applications ranging from ultrafiltration to reverse osmosis. The polymer composites maintain the transport properties critical for water treatment, with the additional benefit of electrical conductivity. We use the membrane’s intrinsic electrical conductivity to solve many of the fouling problems associated with membrane processes. For example, we demonstrate how an alternating current applied to an RO membrane surface prevents the growth of a biofilm; how the application of a DC potential prevents the nucleation and growth of CaSO₄ and CaCO₃ mineral scale; and, how membrane surface potentials can be manipulated to prevent the deposition of organic foulants during the ultrafiltration of concentrated waste streams, such as the effluent from anaerobic reactors. Furthermore, we discuss the energy requirements of our technology, and its potential application in real-world water treatment processes.