Capacitive deionization (CDI) is an attractive environmentally-
friendly technology for removal of hardness ions
consuming relatively small energy, and it does not require any
secondary regeneration wastes, expensive membranes, and
high pressure pumps. In a configuration of CDI cells, the feed
solution flows between each pair of high capacity electrodes,
i.e., porous carbon electrodes. By polarizing both electrodes,
the charged ions are adsorbed on each electrode surface;
positively charged ions are attracted on a surface of the
negatively charged electrode and vice versa