then the resulting cnf cnt composite electrode is subjected to acid treatment and heat treatment to obtain the final cnf cnt composite electrode for a cdi apparatus capable of improving the efficiency of the cdi apparatus this manufacturing process is carried out under the same conditions as in the manufacturing process of the carbon fiber electrode according to the preferred embodiment of the present invention thus a more detail thereof will be omitted hereinafter a cdi apparatus using the carbon fiber electrode and or carbon nanotube composite electrode manufactured prepared in accordance with the afore mentioned method will be illustrated the technology called capacitive deionization cdi is based on a simple principle that when a voltage is applied across two electrodes of a positive electrode and a negative electrode negative ions are electrically adsorbed on the positive electrode and positive ions are electrically adsorbed on the negative electrode to remove the ions dissolved in a fluid such as water in accordance with the cdi when the ions are saturatedly adsorbed on the electrode they can be readily desorbed by reversing the polarity of the electrode thus making it simple to recycle the electrode unlike other methods such as an ion exchange resin method and reverse osmosis the cdi does not employ a cleaning solution e g an acid or a base for the purpose of recycling the electrode thus advantageously being free of the secondary production of chemical wastes the cdi has great advantages of a semi permanent.