REMOVING SYSTEM OF OXIDE NITROGEN IN WATER

PROBLEM TO BE SOLVED: To efficiently and stably remove oxide nitrogen by preventing the interference of the action of a catalyst from occurring from insoluble or hardly soluble metallic compounds produced from metals dissolved in water at the time of reducing and removing the oxide nitrogen in water with the catalyst. SOLUTION: A system provided with an oxide nitrogen removing device 2 and a metal removing device 4 installed at the upstream side thereof is used. In the oxide nitrogen-removing device 2, nitrate nitrogen and/or nitrite nitrogen in a water to be treated are removed by allowing nitrate nitrogen and/or nitrite nitrogen contained in the water to be treated to react with dissolved hydrogen under the presence of the catalyst of reducing nitrate nitrogen and nitrite nitrogen. In the metal removing device 4, the dissolved metals capable of forming compounds insoluble or hardly soluble in the water to be treated is removed from the water to be treated at the upstream side of the oxide nitrogen removing device 2.