Engineers at LLNL are developing revolutionary desalination technologies that use electricity to remove salt from water using a process called capacitive deionization (CDI).
Using electricity as an efficient desalination technique
CDI removes salt from water using an applied voltage to reversibly adsorb and desorb ions from the surface of a capacitor. After charging the cell, desalinated water inside the capacitor can be swept out for collection. During discharging, a portion of the capacitive energy can be harvested and used to power further desalination.
CDI is fundamentally more energy efficient for treating low salinity brackish water than traditional desalination technologies because it operates at low pressure and can reuse energy stored during the desalination process.
CDI performs efficiently even at small scale, and is ideally suited to treat water in remote locations.
Pioneering a flow-through electrode design for CDI
The CDI devices under development at LLNL are made from carefully engineered hierarchical carbon aerogel monoliths (HCAMs). These materials have good electrical conductivity due to their monolithic nature, ample micrometer-sized macropores for allowing water to flow freely through the electrode itself, and high internal surface area due to numerous sub-nanometer pores created by the activation process. The flow-through electrode (FTE) design pioneered by LLNL has the advantage of maintaining high charge efficiency (ions removed/electrical current) without the use of expensive membranes.
Operating a CDI device to achieve optimal throughput and energy efficiency for a given desired separation is non-trivial. At LLNL, we work extensively on understanding how operation-mode physics impacts device performance and long-term stability. We have recently pioneered concepts ranging from understanding CDI cycling charge efficiency to how to properly define relevant performance metrics.
Selective ion removal
Another major application of CDI is for selective ion removal. We are developing operation modes and engineered carbon materials for the purpose of selectively removing nitrate and hardness (calcium, magnesium). By tuning our material pore structure, we have demonstrated exceptional intrinsic selectivities for nitrate over common interferent ions like chloride and sulfate.
For information about licensing LLNL CDI technology, please contact Annemarie Meike (meike1 [at] llnl.gov).
