PROBLEM TO BE SOLVED: To provide a method and an apparatus for disinfecting wastewater containing ammoniacal nitrogen by adding a disinfectant having excellent handleability. Immediately after preparing a disinfectant containing hypochlorous acid by dissolving a predetermined amount of a solid hypochlorous acid source (B) in a drug (A) containing bromine ions, the disinfectant is ammoniacal. Disinfection method to add to nitrogen-containing wastewater, mixing part 1 to add solid hypochlorous acid source (B) to drug (A) and mix, accepting mixture from mixing part 1 and hypochlorous acid to drug (A) Disinfectant preparation unit 2 that dissolves the chloric acid source (B) to prepare the disinfectant, the first line 3 that supplies the disinfectant (A) to the disinfectant preparation department 2, and the disinfectant immediately after preparation from the disinfectant preparation department A disinfectant device including a disinfectant supply line 4 for supplying the waste water containing ammonia nitrogen. [Selection diagram] Fig. 1【課題】取り扱い性に優れた消毒薬をアンモニア性窒素含有排水に添加して消毒する方法及び装置を提供する。【解決手段】臭素イオンを含む薬剤（A）に所定量の固体の次亜塩素酸源（B）を溶解させて、次亜塩素酸を含む消毒薬を調製した直後に、消毒薬をアンモニア性窒素含有排水に添加する消毒方法、及び薬剤（A）に固体の次亜塩素酸源（B）を添加して混合させる混合部１、混合部１から混合物を受入れて薬剤（A）に次亜塩素酸源（B）を溶解させて消毒薬を調製する消毒薬調製部２、消毒薬調製部２に薬剤（A）を供給する第１ライン３、消毒薬調製部２から調製直後の消毒薬をアンモニア性窒素含有排水に供給する消毒薬供給ライン４を具備する消毒装置。【選択図】図１
