Fresh water scarcity plagues billions of people worldwide. In order to combat this issue, unconventional sources such as seawater and municipal wastewater are needed to supplement the water supply. To make these water sources potable, scientists employ reverse osmosis (RO), the process by which water is passed through a semipermeable membrane to remove ions and particles, as a desalination technique. Polyamide RO membranes are by far the most successful technology in terms of permeability and salt rejection. However, they have one major pitfall: susceptibility to chlorine degradation. Thus, a team of researchers, led by Yale Professor of Chemical and Environmental Engineering Menachem Elimelech, Ph.D. candidate Ryan DuChanois, and visiting professor Xuan Zhang, have designed a polyester RO membrane, inspired by chlorine-resistant swimsuits, that circumvents chlorine degradation while maintaining high purification standards.
The team’s RO membrane comprises four layers: a bottom layer of polyethersulfone, a nanofiltration layer, and two polyester layers. The polyester forms through interfacial polymerization, a process in which monomers in immiscible (unable to mix homogeneously) solutions react. “This process is an excellent way to make thin desalination membranes with no defects. Membranes need to be thin for high water permeability and also defect-free for high salt rejection,” DuChanois explained. The polyester membrane is also highly effective due to its oxidative stability thanks to its strong steric hindrance and ester linkages; both of these factors, amongst others, serve to increase the membrane’s chlorine resistance. Chlorine is often used to clean and prevent biological buildup in water supply, so a membrane immune to degradation by chlorine allows for longer lifespan and cost-effectiveness. Speaking to the promise of their research, DuChanois says that such an effective chlorine-resistant RO membrane has been highly sought after. Their technology can withstand environmental and chemical factors, maximizing the lifespan and potential of these membranes for commercial use.