With multilayered approach, a filter to meet freshwater supply needs

In search of a better way to desalinate water, a Yale-led team of researchers has turned to swimsuit material for inspiration. 

Reverse osmosis, which uses membranes to remove unwanted salts, has been the gold standard for desalination and wastewater reuse. The challenge that scientists have run into, however, is that the material that best filters out impurities — polyamide — is highly susceptible to chlorine. Although chlorine is typically useful in cleaning membranes, it can degrade membranes made from polyamide. 

Scientists at Yale and Nanjing University of Science and Technology have created a chlorine-resistant membrane — what the researchers call “the holy grail of the industry” — that could significantly advance the field to better meet global water supply challenges. Results of their work, led by Yale’s Menachem Elimelech, the Roberto C. Goizueta Professor of Chemical & Environmental Engineering, were published Oct. 5 in the journal Nature Sustainability.

With their fabrication methods, Elimelech said, they’ve created a scalable technology for robust reverse osmosis membranes that has the potential for low-cost production necessary for large-scale, real-world application.

“These membranes may enable a more economically and environmentally sustainable way to desalinate and reuse wastewater, and meet freshwater supply needs in the 21st century,” he said. 

A key component was the choice of material. “We’re using a polyester membrane,” said Ryan DuChanois, a graduate student in Elimelech’s lab. “One of our inspirations was swimsuits, which are made from polyester materials, and obviously, those are chlorine-resistant.”

The use of polyester has been considered previously, without success. Those earlier polyester membranes did not had the same ability to reject salt as a polyamide membrane. This led the research team to try a multilayered approach. 

“We took the first layer, which is a conventional nanofiltration membrane that is susceptible to chlorine attack and then on top of that, we put polyester layers,” said Xuan Zhang, a professor at Nanjing University of Science and Technology. “If we only used the polyester layer and not the nanofiltration layer, it wouldn’t form a dense reverse osmosis membrane, so the formation of the polyester occurring inside the pores of the nanofiltration membrane was critical to creating a reverse osmosis membrane.”

Not only did the multilayer membrane prove resistant to chlorine, it performed as well as the conventional polyamide membrane in terms of water permeability and desalination performance. 

“People have been trying for a long time to find chemistry for a reverse osmosis membrane that’s also chlorine-resistant,” DuChanois said. “We’ve known how to tackle one or the other, but not both together, so the fact that we took a chlorine-resistant material and made it into a reverse osmosis membrane was exciting.”

Zhang said the researchers will work on optimizing the technology to make it scalable for industry use. 

“We’ll evaluate some other properties of the polyester membrane and attempt to further simplify the membrane fabrication method to meet the need of industrial processing,” Zhang said.