Carbon aerogel capacitive deionization (CDI) was developed as a non-polluting, energy-efficient, and cost-effective alternative to ion exchange, reverse osmosis, electrodialysis, and evaporation. This process offers dramatic advantages in terms of both waste minimization and reduced processing costs for the Department of Defense (DoD) and the Department of Energy (DOE).

The objective of this project was to design and document the continuous-flow potential-swing system of carbon aerogel CDI.

The technical approach for the design and documentation of the continuous-flow potential-swing carbon aerogel CDI system included the following: (1) carbon aerogel and electrolysis proof-of-principal testing; (2) patenting of the process; (3) development of a fully-automated, continuousflow potential-swing CDI process; (4) model development and engineering analysis of the process; (5) enhanced electrosorption capacity of the existing potential-swing CDI system; (6) demonstration of the technology at selected DoD sites; and (7) documentation of the hardware, software, and results in various publications.

Electrodes for the carbon aerogel CDI prototype were made from thin sheets of carbon aerogel composite, a novel material developed at Lawrence Livermore National Laboratory, Livermore, CA, that has a high specific surface area and an exceptionally low electrical resistivity. Arrays of the electrodes, gaskets, and spacers were used to create electrode stacks. Sensors were placed on the inlet and outlet lines of the electrode stack, and open-channel electrical flow was generated through the stack. Electrical conductivity of the solution, pH, individual ion concentrations, and temperature were monitored continually, and a computerized data acquisition system logged these operating parameters. Through preliminary engineering analysis of the process, it was determined that the carbon aerogel CDI is inherently energy efficient.

The fully-automated, continuous-flow potential-swing CDI process was developed. This work enabled the carbon aerogel CDI prototype to produce a continuous flow of both product water and concentrate by operating two stacks of carbon aerogel electrodes in parallel.

Treatability studies were conducted. At Aberdeen Proving Grounds, MD, it was shown that carbon aerogel CDI, proceeded by UV-H₂O₂ oxidation, could be used to treat the aqueous effluent from bioreactors where mustard gas is destroyed. Such treatment could be used to make water recycle possible during the destruction of chemical warfare agents. At Tyndall Air Force Base, FL, carbon aerogel CDI was used alone as a means of removing NH₄CLO₄ from water. In the case of foaming agents, UV-H₂O₂ was used to mineralize the organic surfactants, thereby enabling the removal of residual inorganic ions by CDI. Additionally, trace heavy metals were removed from proces s solutions and natural waters by electrodeposition and electrophoretic deposition on the carbon aerogel electrodes. Tests were also conducted at the Berkley Pit in Buette, MO, demonstrating the effectiveness of the carbon aerogel process for treating heavy metals from the site. This project was completed in FY 1996.

The potential benefits of this project include the elimination of secondary wastes associated with the chemical regeneration of ion exchange columns and the elimination of costly and troublesome membranes and high-pressure pumps. Associated benefits include a reduction in energy consumption and waste reduction processing and the development of a possible low-cost reclamation process for the desalination of brackish water.