[PERSON]  
1 Department of Environmental Engineering, University of Seoul, 163 Seoul'siripdaero, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS] (J.Y. ); [EMAIL_ADDRESS] (Y.A. ); [EMAIL_ADDRESS] (G.-H.K. ); [EMAIL_ADDRESS] (N.S.) [PERSON]  
1 Department of Chemical Engineering, Hanyang University, 222, Wangsimi-ro, Seongdong-gu, Seoul 04763, Korea; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (B.J. ); [EMAIL_ADDRESS] (B.-I.S.) [PERSON]  
1 Department of Chemical Engineering, Hanyang University, 222, Wangsimi-ro, Seongdong-gu, Seoul 04763, Korea; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (B.J. ); [EMAIL_ADDRESS] (B.-I.S.) [PERSON]  
1 Department of Environmental Engineering, University of Seoul, 163 Seoul'siripdaero, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS] (J.Y. ); [EMAIL_ADDRESS] (Y.A. ); [EMAIL_ADDRESS] (G.-H.K. ); [EMAIL_ADDRESS] (N.S.) [PERSON]  
1 Department of Chemical Engineering, Hanyang University, 2222, Wangsimi-ro, Seongdong-gu, Seoul 04763, Korea; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (B.J. ); [EMAIL_ADDRESS] (B.-I.S.) [PERSON]  
1 Department of Chemical Engineering, Hanyang University, 222, Wangsimi-ro, Seongdong-gu, Seoul 04763, Korea; [EMAIL_ADDRESS] (M.H. ); [EMAIL_ADDRESS] (B.J. ); [EMAIL_ADDRESS] (B.-I.S.) [PERSON]  
1 Department of Environmental Engineering, University of Seoul, 163 Seoul'siripdaero, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS] (J.Y. ); [EMAIL_ADDRESS] (Y.A. ); bluemelon33@gmail. Chlorine not only exerts toxic effects on adult organisms but also inhibits the growth of larvae and their attachment to the substratum [6; 7]. There are various methods to make chlorine in water, such as (i) dissolution of chlorine gas; (ii) addition of hypochlorite; and (iii) electrolysis of electrolytes containing salt or seawater (i.e., electrochlorination) [8]. Anode  
\[2\;\mathrm{Cl}^{-}\leftrightarrow\mathrm{Cl}_{2}+2\;\mathrm{e}^{-}\;\mathrm{( E_{o}=1.36\;V)} \tag{1}\]  
Bulk solution  
\[\mathrm{Cl}_{2}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{H}^{+}+\mathrm{Cl}^ {-}+\mathrm{HOCl} \tag{2}\]  
\[\mathrm{HOCl}\leftrightarrow\mathrm{OCl}^{-}+\mathrm{H}^{+}\;\mathrm{(pK_{a} =7.5\;at\;25\;^{\circ}C)} \tag{3}\]  
\[\mathrm{HOCl}+\mathrm{H}^{+}+\mathrm{e}^{-}\leftrightarrow 1/2\;\mathrm{Cl}_{2}+ \mathrm{H}_{2}\mathrm{O}\;\mathrm{(E_{o}=1.63\;V)} \tag{4}\]  
\[\mathrm{NaCl}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{NaCl}+\mathrm{H}_{2} \tag{5}\]  
Cathode  
\[\mathrm{O}_{2}+2\;\mathrm{e}^{-}+2\;\mathrm{H}^{+}\;\mathrm{\rightarrow}\; \mathrm{H}_{2}\mathrm{O}_{2}\;\mathrm{(E_{o}=0.68\;V)} \tag{6}\]  
\[2\;\mathrm{H}_{2}\mathrm{O}+2\;\mathrm{e}^{-}\;\mathrm{\rightarrow}\;2\; \mathrm{OH}^{-}+\mathrm{H}_{2} \tag{7}\]  
Currently, the ex situ electrolytic production of hypochlorite, which is subsequently injected into pipes, is commonly carried out in practice. Compared with ex situ electrochlorination, in situ electrochlorination in seawater has a few advantages. This does not require supply of NaCl since it uses Na\({}^{+}\) and Cl\({}^{-}\) in seawater as electrolytes. In addition, it does not require any space for hypochlorite generation and storage. Therefore, in situ electrochlorination should be more economical than ex situ. Generally, the residual chlorine concentration of water flowing through the pipe of a cooling system is maintained at 0.2 mg/L or higher to control biofouling [14; 15; 16]. In practice, chlorine is added in the inlet of the cooling system and the chlorine concentration at the inlet is varied depending on its level at the outlet [17]. In fact, a large amount of seawater is withdrawn for the cooling system in a power generation system (e.g., 95-230 m\({}^{3}\)/MWh for the once-through cooling system of a nuclear power plant [15; 18]). So, an enormous amount of chlorine should be applied in the inlet. Chlorine exerts a biocidal action on microorganisms in water by oxidizing enzymes responsible for microbial growth.