Steps in Planning the Expansion of the Large Sewage Treatment Plant at Buchenhofen, Operated by the Wupper Watershed Management Association
Sewage from 700,000 PE, roughly half of which is discharged by industry, is treated at the Buchenhofen plant operated by the WWMA, using a conventional, activated-sludge process without specific nutrient elimination. A draft management plan has been prepared for the receiving stream of the treatment plant, the Lower Wupper. The chief forms of use for the waters are fixed in binding agreements. The use entailing the strictest limiting values is recreational fishing, which demands surface water quality class II. Very substantial demands, which must be regarded as at least equivalent to state-of-the-art technology, are imposed on the Buchenhofen facility. The Institut für Siedlungswasserbau, Wassergütewirtschaft und Abfalltechnik at the University of Stuttgart was commissioned to formulate realistic purification objectives for the treatment plant and to prepare expansion concepts. At Buchenhofen, the single-stage activated sludge process with nitrification and preliminary de-nitrification has proved to be the most effective method for eliminating nitrogen while simultaneous precipitation followed by flocculation-filtration is the best process for eliminating phosphorus. For purely scientific reasons, however, the extreme demands in terms of ammonium and nitrite rule out expansion of a treatment plant of this size. The proposed designs therefore require validation through commercial-scale testing. Only after a 6- to 12-month test series has been evaluated will a draft design be prepared for approval, ultimately enabling the plant to be expanded and to fulfil the management planning objective of achieving surface water quality class II in the Wupper.