carbon electrodes or cnf cnt porous carbon electrodes 50 a and 50 b thus manufactured to a cdi apparatus the electrodes 50 a and 50 b are made to a size of 10 cm u00d7 10 cm and a cid system consisting of 20 cells is then obtained the electrodes are designed to be spaced apart from each other at a distance of 1 mm using a spacer not shown graphite is used as a collector when a voltage of 0 to 1 2 v is applied to the positive electrode negative ions are adsorbed on the positive carbon electrode 50 a and positive ions are adsorbed on the negative carbon electrode 50 b at this time when hard water of 1 000 ppm is treated at a flow rate of 100 ml min an ion removal ratio and an ion recovery ratio are 90 and 70 respectively the carbon nanofiber electrode and carbon nanotube composite electrode according to the method of the present invention may be used in the field of water treatment including sea water desalination facilities water purifying plants wastewater utilities semiconductor wastewater treatment utilities water purifiers water conditioners washing machines dishwashers air conditioners water suppliers of water quenching heat exchangers steam cleaners boiler scale control facilities.