Salt-Water-Organic Transport Nexus and Mechanisms through Cation Exchange Membranes: Effect of Membrane Sulfonation Degree

Organic permeation through an ion exchange membrane is an urgent problem to be solved in electrodialysis (ED) processes on treating industrial wastewaters. However, how the salt, water, and organic compounds co-transport in an ED stack is still unclear. To reveal this, a series of cation exchange membranes (CEMs) were prepared in this work by using sulfonated polysulfone with different sulfonation degrees as a tool to “adjust” membrane water uptake and “control” water migration. The results showed that CEMs with a high sulfonation degree had positive correlation with desalination performance. Salt migration led to organic matter migration, while the presence of small molecule organics reduced the water flux and elevated the sodium flux, which favored the ED process. It was proven that the membrane sulfonation degree could be an important tool to adjust water permeation, and as a consequence, to improve the separation performance of salt from organic compounds in wastewater.