Method and device for manufacturing sodium hypochlorite solution

A production method of a sodium hypochlorite solution for producing a sodium hypochlorite solution on-site in the vicinity of a physical plant where a sodium hypochlorite solution is used, comprising:

• in production of a sodium hypochlorite solution by feeding secondary salt water as an aqueous sodium chloride solution, in an electrolyzer comparted into an anode chamber and a cathode chamber with an ion-exchange membrane, to the anode chamber and, after electrolysis, introducing an anolyte and generated chlorine gas in the anode chamber and an aqueous sodium hydroxide solution generated in the cathode chamber into a reaction tank, to allow the anolyte, the chlorine gas, and the generated aqueous sodium hydroxide solution, as a catholyte, to react in the reaction tank,
• a cation exchange step of generating purified water by treating raw material water with a cation-exchange resin;
• a primary salt water generation step of generating primary salt water by dissolving raw salt containing sodium chloride as a main component in the purified water;
• an examination step of performing an examination for confirming the presence or absence of a precipitate or suspended solid in the primary salt water;
• and
• a chelating step of performing chelating in the case of no precipitate or suspended solid contained in the primary salt water, or performing chelating after addition of an acid component for dissolution of the precipitate or suspended solid in the case of the precipitate or suspended solid contained in the primary salt water, to generate the secondary salt water.