TREATMENT OF WASTE WATER

PURPOSE:To release treated waste water with good quality in a stage for treating the waste water by a biological memberene method, by aerating excessively the waste water temporarily from an ordinary aeration state to remove forcibly the biological membrane periodically from a contact base material. CONSTITUTION:Waste water 1 to be treated is introduced into a treatment tank 2, where the water is subjected to a biological membrane treatment. The treated water 3 is fed to a settling tank 4, where the water is subjected to a solid- liquid sepn. The separated water is released as release water 8. Plural net-like contact base materials 5a-5d are packed in the tank 2, and when the qualtity of the water 8 begins to deteriorate, an excess amt. of air is ejected simultaneously from all the air diffusion pipe 7 groups of an air diffuser 6 attached to the materials 5a-5d to aerate the materials. The biological membrane of the decreased degree of activity sticking to the net-like contact base material are forcibly removed and are made to the fresh biological membrane having a high degree of activity to activate the treatment, whereby the quality of the water released from a settling tank 4 is improved.