Intermediate pumping station
The wastewater flows from the first biological cleaning stage into the lower chambers of the intermediate pumping station, from where it is lifted to the plant level of the second biological cleaning stage by vertical propeller pumps. The return sludge that is withdrawn from the second-stage sedimentation tanks is channelled into a separate lower chamber and also lifted to the level of the second stage by vertical propeller pumps so it can flow by gravity through the second biological stage along with the wastewater from the first stage. In the upper chamber, both wastewater streams merge and flow together towards the mixer and the distribution chamber. The wastewater-return sludge mixture flows through two mixer units assembled from single steel plates. This structure deflects the flow and assures a homogeneous blend. Inside the distribution chamber, the wastewater-sludge mixture is distributed among the 15 aeration tanks of the second biological cleaning stage. To assure identical streams, each aeration tank has an inlet pipe which is equipped with a flow meter and a flow control gate.