To provide a biological denitrification apparatus for easily carrying out prevention of an outflow outside a tank and maintenance management of a concentration in the tank in causing reaction with autotrophy denitrifying bacteria to carry out denitrification treatment. 独立栄養性脱窒菌と反応させて脱窒処理を行うにあたり、槽外への流出防止と槽内濃度の維持管理を容易に行う生物脱窒装置を提供する。 - 特許庁