The world's freshwater resources are in short supply. According to the United Nations, water scarcity affects an estimated 1.9 billion people and 2.1 billion people live with drinking water services that are not safely managed. The critical point of water scarcity has led scientists to look for new and efficient ways to make the most of nontraditional sources, including sea water, brackish water and wastewater.

Polymer membranes, which act as a filter to desalinate and selectively remove contaminants from various water sources, have aided water treatment, but their selectivity remains a significant challenge when it comes to filtering chemical properties -- a potential risk to the environment and human health.

Chemical and biomolecular engineers at the University of Notre Dame and Purdue University studied self-assembled block polymer membranes, which allow for both customizable and uniform pore sizes, as a platform for water treatment systems. The study, published in Nature Partner Journals -- Clean Water, determined the platform has the potential to advance water treatment technologies.

"Most state-of-the-art membranes for water treatment are designed to let water pass through while filtering contaminants," said William Phillip, associate professor in the Department of Chemical and Biomolecular Engineering at Notre Dame. "This approach limits the ability to remove or recover dissolved species based on their chemical identity. The exciting thing about self-assembled block polymer membranes is that you can engineer the nanostructure and pore wall chemistry of the membrane through the design of the block polymer molecules. This capability has the potential to open up a variety of new separation mechanisms that can isolate species based on chemical identity, which in turn could help to enable decentralized reuse of wastewater."

Phillip and the research team focused on block polymer membranes because of their well-defined nanostructures and functionality. They were able to molecularly engineer the chemical properties of the polymer to create large areas of high-performance membrane, reduce pore size and design multifunctional pore wall chemistries for solute-specific separation. The membranes could essentially be customized depending on the water source and treatment needed.

Membranes that are more selective and more resilient to certain exposures such as chlorine or boric acid and less prone to collecting unwanted properties -- or fouling -- than current state-of-the-art options could improve treatment in a number of ways. They could reduce the number of filtration passes required for irrigation, control concentrations of chlorine into the system to help forestall effects of biofouling and reduce chemical demands for membrane cleaning -- reducing operating costs and environmental impact.

The global applications are significant when considering those populations without suitable drinking water and limited resources.

Transitioning the technology from the laboratory setting to practice presents its own set of challenges that will need to be addressed in the coming years. However, the researchers are hopeful the transition can be made since several of the techniques used to generate self-assembled block polymers are consistent with current membrane fabrication practices.