Treatment of Filter Effluents from Dewatering of Sludges by a New High Performance Flocculation Reactor

Abstract

For the removal of turbidity and phosphorous, a flocculation aid must be added to turbid water. With current techniques, the formation of macroflocs requires between 10 and 60 min. Only a small area was available for the treatment of a filter effluent from dewatering of sludges produced by de-sludging of a lake. Therefore a cylindrical stirred tank was used that was characterized by the same narrow distribution of local velocity gradients and residence times as a new flocculation reactor. In order to achieve the water quality required for discharge into the lake (Cak = 2 FTU, c(P T) = 0.06 mg/l), a total mean residence time of only 14 min is sufficient (0.5 min for precipitation and coagulation in a tube reactor, 2 min for flocculation in the cylindrical stirred reactor and 11.5 min in a lamella separator). The filter effluent of about 60 m3/h was treated for nearly two years without any trouble.