Sewage Purification and Sludge Treatment Systems Sewage Treatment Plant, Unterföhring, Extension for Phosphorus and Nitrogen Elimination Project period 1993 - 2000 Construction cost 600 000 mio. € approx. Services provided Project planning, tendering site supervision, construction management and commissioning, planning and construction management of the proc- ess, procedure and electronic instrumentation technology Technical details Extension of the existing mechanical-biological sewage treatment plant with anaerobe sludge treatment for the elimination of phosphorus and nitrogen Size of extension: 20 000 population units This combined mechanical and bio- logical treatment plant went into operation in 1981. In 1993, the up-grading of the legal and water-management require- ments governing the elimination of nutrients called for the installation of a simultaneous precipitation plant, followed in 1997 by the adoption of measures to reduce the nitrogen burden. After inspecting the different plant extension alternatives for nitrogen elimination for technical and com- mercial viability, the municipality decided in favour of the carrier- material method. The use of carrier material makes it possible to in- crease the amount of micro- organisms in each tank, thereby improving the purification power of the sewage plant. This means that a reduced tank volume is sufficient for purposes of nitrification. The extra tank volume made avail- able in this way was separated off by means of stainless steel walls, and is being used as a preliminary denitrifi- cation tank to further increase the removal of nutrients. Apart from this, the preliminary sedimentation tank was made smaller, with part of it being used for denitrification and biological elimination of phosphorus. The carrier-material method meant that structural extensions in the form of an extra activated sludge tank could be dispensed with. The extension of the sewage plant for purposes of nitrogen elimination furnishes values well below the run- off works required by water man- agement regulations, resulting in an additional reduction in the amount of effluents discharged.
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