To provide a wastewater treatment apparatus, in which even in high BOD waste water, nitrous acidizing anaerobic denitrification treatment can be efficiently performed by a simple apparatus constitution, and which can be applied to a continuous type and a batch type. 高BOD廃水でも、亜硝酸化嫌気性脱窒処理を簡単な装置構成で効率よく行うことができ、連続型にも、バッチ式にも適用が可能な廃水処理装置を提供する。 - 特許庁