This study examines the possibility to optimally produce active chlorine from a synthetic concentrate of seawater by electrolysis using an experimental design methodology. Different operating parameters were investigated such as current density, reaction time, hydrochloric acid concentration and chloride ion concentration. Using a 2(4) factorial matrix, the best performance for active chlorine production (46 mg/l of HClO) was obtained at a current intensity of 1.6 A during 35 min of treatment time in the presence of 0.11 M of H3O+ and 0.8 M of NaCl. The current intensity and treatment time were the main parameters influencing the active chlorine production. Subsequently, a central composite design methodology has been investigated to determine the optimal experimental parameters for chlorine production. The electrolytic cell applied under optimal conditions (at a current intensity of 1.6 A during 27 min in the presence of 0.11 M of NaCl and 0.8 M of H3O+) is able to produce 31 mg/l of chlorine for an energy consumption of 0.54 kWh/m(3). (C) 2012 Elsevier B.V. All rights reserved.