At the Seehausen Sewage Works, the sewage arising from the City of Bremen is treated. The maximum dry weather sewage flow is about 150,000 m3/d; under storm weather conditions the maximum flow is 300,000 m3/d. The existing plant consists of a primary sedimentation followed by a two stage activated sludge plant. Waste sludge is treated in 5 anaerobic digesters followed by dewatering centrifuges. At present, the plant achieves full removal of the BOD5, however no nitrification.In accordance with the new German water laws and with respect to the eutrophication problems encountered in the North Sea, both nitrogen and phosphorus removal are required in the future. This paper describes the measures planned to enlarge the volume of the activated sludge plant for nitrification/denitrification and measures for biological phosphate removal by means of anaerobic basins. A new single stage activated sludge plant for 50% of the total sewage flow will be built. After completion of this plant, it will be operated in parallel with the existing two stage plant. Both, the old and the new part of the plant, will provide nitrification and denitrification. In addition, the new plant is designed for biological phosphorus removal. The existing secondary clarifiers will be connected to both plants at 50% each.
