At both two-stage activated sludge treatment plants of the city of Frankfurt an almost complete nitrification is achieved. Upgrading of the plants is required to ensure denitrification. As an alternative for implementing a solution according to the German ATV-Standard A 131 separate denitrification by an upflow fluidized-bed technology was thoroughly investigated on pilot plant scale. The results show, that a far-reaching denitrification can safely be obtained by this process. Equations for quantifying the volumetric denitrification capacity of the bed (kg ΔN/m3·d) and the effluent nitrate concentration are derived for process design. The denitrification efficiency of the system, its benefits and disadvantages are discussed together with economical aspects.

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