Large quantities of wastewater containing suspended solids, heavy metals and particularly ammonium are derived when disposing of the dredged material from the Hamburg harbour. For the first time, a state-of-the-art method of purifying this wastewater comprising the following stages has been defined and realised: recirculation of transport-water in order to reduce quantities, flocculation followed by sedimentation to remove the suspended solids, and nitrification in a combination of trickling filters and rotating biological contactors. The main results of the first two years of operation are presented. Suspended solids are removed to 80% and heavy metals to between 60 and 90%; the COD is reduced from up to 250 mg/l to approx. 60 mg/l and ammonium inflow values of up to 80 mg N/l are reduced to values smaller than 2 mg N/l at temperatures above 10 °C. At 10 °C the nitrification rates reach values of up to 0.55 g NH4-N/m2 d in the trickling filter and up to 1.40 g NH4-N/m2 d in the rotating biological contactor. An expert system is used for operating the nitrification stage.

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