Steam stripping and nitrification/denitrification for the elimination of nitrogen from sludge treatment reject water from the Central Sludge Treatment Facilities (CSTF) of the Emschergenossenschaft in Bottrop were tested in half-scale pilot plants. More than 90% efficiency could be achieved with both systems; the nitrification/denitrification process also removed organic nitrogen. Operational experience has shown that full scale application of both systems is possible. The design surface load of the stripping column has been evaluated as 10 m3/(m2*h) and the steam/water ratio as 0.12 t/m3. The nitrification/denitrification process can be designed for 0.07 kgN/(kg MLSS*d) and 1.4 days hydraulic retention time. Total treatment costs are estimated to be between 5 and 7.5 DM/kg N.

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