Biological sewage treatment plant

Abstract

Biological sewage treatment plant comprising at least one treatment or aeration tank (1, 2, 3,) for the biological process, having an inlet (6, 7) for sewage, an outlet (14, 8) for treated water and a conduit (1, 2, 3) for air supply down in each treatment tank. There is also provided a settling tank (4) with a conduit (10) for feeding back sludge from the bottom thereof to a preceeding treatment tank (1), said air supply conduit in each treatment tank (1, 2, 3) being provided with its outlet (1A, 2A, 3A) adjacent to a vertical wall in the treatment tank. A baffle plate (11A, 12A, 13A) extends from a level above the operational water level in the treatment tank at an inclination downwards-inwards towards a vertical wall part in the tank opposite said vertical tank wall, for establishing a clarifier chamber (11, 12, 13) which is separated from the main part of the tank, but communicates with the latter through a lower opening in the clarifier chamber. The clarifier chamber has a volume which constitutes a small fraction of the total volume of the treatment tank. All treatment tanks (1, 2, 3) are arranged end to end in the longitudinal direction of the process, and the outlet from each treatment tank is provided in the form of an overflow sill (16, 17, 18) from the clarifier chamber (11, 12, 13) to the following treatment tank (2, 3 and 4 respectively), said overflow sill being formed completely or in part by a substantially horizontal edge at the top of the wall between (1A, 2A, 3A) for air two successive tanks (1, 2, 3, 4).