Existing technologies for hard, brackish and sea water desalination are highly energy consuming even in the case of the best available technology nowadays, Reverse Osmosis. In addition to this problem, the construction of desalination plants requires intensive capital expenditures.
Capacitive Deionization is a technological alternative to Reverse Osmosis provided it is a non-membrane and low-pressure process, which are possibly the two main drawbacks of the Reverse Osmosis technology. The Capacitive Deionization concept is schematically represented in the Figure. During the deionization cycle, an external electrical charge is applied on a pair of electrodes introduced in the feed water, this makes the ions dissolved in the water to migrate towards the electrode of opposite charge, where they are adsorbed. In the regeneration cycle, the electrical load of the electrodes is switched off, therefore adsorbed ions are released. If an electrical circuit is connected at this stage, an electrical current will be produced, just like in the discharge of a capacitor.