Treatment of Effluent from Dredged Material Disposal Sites: Suspended Solids Removal and Nitrification

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.