In this study, I would like to remove a residual chlorine in seawater link with the study to have practical use wastewater treatment process of circulating filterable acuaculture. Form of activated carbon which is selected to be suitable in circulating filterable process is a granular activated carbon, and the specific character of residual in activated carbon diameter and hydraulic residence time, early concentration of wastewater is experimented in a continuous fixed reactor. In addition, the specific character of residual chlorine reaction of activated carbon particle with time is experimented in a batch reactor. And the experimental result is considered in comparision with adsorption and reactive mechanism of residual chlorine. As an experimental result, A removal residual chlorine was showed to be different usual adsorption, and removal efficiency increased by being small of free chlorine and actived carbon diameter, by raising hydraulic residenec time. Removal of residual chlorine by activated carbon was showed a lot higher removal efficiency, and considered to be effective in removal of unreacted residual chlorine.