Electrical Energy Processes
Electrical energy processes utilize and electrical current to draw solutes out of solution. Electrodialysis (ED) is the most common electrical energy desalination method. Processes that attempt to take advantage of the movement of ions in an electrical field include electrodialysis, electret technology, and capacitive deionization., :
- Electrodialysis, ED for short, can be described, in the most general terms, as a process that moves ions (charged molecular species) from one solution to another, employing an electrical potential as the driving force and using some sort of semi-permeable membrane as a separator. This process can be used for concentration, dilution, or segregation of ionic species. The classical reference on electrodialysis of water, for breadth of approach and depth of research, is the book by Wilson (Wilson, 1960).
A primitive form of electrodialysis has been used for salt removal from solutions since the beginning of the twentieth century, primarily in the laboratory. With the invention of the synthetic ion-exchange membrane in 1948, it became a practical means for water desalination. Electrodialysis was publicly demonstrated in 1952 (Lawrence, 1952). The introduction of current reversal electrodialysis in the early 1970s made operation with no chemical addition possible. For a more extensive discussion of ED see the reports listed below.
- Other electrical potential driven processes were investigated under the DWPR program. Electret technology relies on static charge to draw dissolved salt ions to the electrodes while the water in the center becomes depleted of salts. It was hoped that the center volume of water could be extracted without disturbing the charge separation. This process only works for very low salt concentrations and very low flows.
- Capacitive deionization is a similar idea except that the electrodes are made of carbon aerogel such that the salt ions are drawn into the structure of the aerogel. This helps to allow the depleted water between the electrodes to be extracted without pulling the ions away from the electrodes. However, when the electrodes are saturated, they need to be regenerated by reversing the polarity of charge on the aerogel. The high surface area of the aerogel works well for absorbing high concentrations of ions, but it is also tenacious in holding them. Experiments showed that it required as much water to flush the electrodes as had been treated in the previous cycle.
- Electrodialysis in Pilot Studies
- Investigation of other Electrical Potential Driven Processes