A research project conducted at the Center for Integrated Nanotechnologies has found that, by mimicking Mother Nature, scientists at Sandia Labs were able to develop a new membrane to make fresh water. By mimicking an algae protein, the membrane can remove salt from seawater and wastewater to make fresh water for farming and energy production, all while using less electricity than the current method. The project was funded by Sandia’s Laboratory Directed Research and Development program.
By adding a common amino acid, called phenylalanine, to an electrodialysis membrane, the researchers discovered it enabled the membrane to better capture and remove positive ions, such as sodium. Susan Rempe, a Sandia National Laboratories bioengineer, and Stephen Percival, a material scientist, shared their membrane design in a paper published recently in the peer-reviewed scientific journal Soft Matter.
Currently, electrodialysis using electrical power is used to capture salt from seawater. This facilitates the removal of salt from brackish water to make fresh water and produce table salt. The new, more efficient membrane could also be used to remove salt from industrial wastewater to provide a new source of fresh water.
“Adding phenylalanine to the electrodialysis membrane increased the selectivity for positive ions by a significant amount, to our pleasant surprise,” lead bioengineer Rempe said.
Ensuring an adequate supply of fresh water is a national security problem, Rempe added. Fresh water is essential for everything from drinking and farming to producing energy from nuclear, coal and natural gas-based power plants.
There are few options for cleaning up salty wastewater. The more concentrated the salty solution, the harder it is to remove the salt. Water that is produced by hydraulic fracturing to recover natural gas can be ten times as salty as seawater. As a result, the produced water generally gets buried underground instead of being returned to the environment, Rempe said.
Due to its salty nature, while some oil and gas operators have been reusing water for energy production, often the produced wastewater is buried underground. The new membrane could be a way to economically desalinate the industry’s wastewater.
“Our University of Texas at El Paso partners analyzed our membrane in a real electrodialysis system,” Rempe added. “They put membrane samples into their lab-scale system, ran a whole bunch of tests and compared our membrane to commercial membranes. Our membrane did quite well.”
For a future research project, Rempe would like to design an electrodialysis membrane that can separate out specific economically valuable ions, such as rare earth metal ions. Rare earth metals are used in automotive catalytic converters, powerful magnets, rechargeable batteries and cell phones and are mostly mined in China.
“Rare earth metals are valuable, and the lack of domestic supply is a national security issue. Together, taking care of our water supply and recycling our valuable minerals are important for environmental security and climate mitigation.” Rempe said.