The behavior of selected chlorinated organic micropollutants in the activated sludge process: A pilot plant study

Abstract

An activated sludge pilot plant was operated at 4, 6, and 9 d sludge ages with influent settled sewage from a full scale treatment works. The behavior of the chlorinated organic micropollutants was examined at their background levels by analysis of influent settled sewage, mixed liquor and effluent by gas chromatographic methods. Highly significant removal at all sludge ages m terms of the reduction m micropohutant concentration in influent sewage to final effluent was observed for dieldrin, PCB, 4-C-3-MPol and dimethylphenol. Significant removal at some sludge ages was observed for Y-HCH, DDE, pentachloro phenol and 2,4-DCPol. Calculated mass balances indicated that removal of Y-HCH, PCB, and DDE was by adsorption onto MLSS rather than by air stripping or a degradative process. A comparison of the effluents from the activated sludge tanks run at 4 and 9 d sludge age with the same influent settled sewage indicated that significantly higher concentrations of pentachlorophenol, 2,3,4,6-TcCPol, 2,4,6-TCPol, and 4-C-2-MPol were seen in the effluent from the unit run at 4 d sludge age. The effluent from the 9 d sludge age tank had significantly higher concentrations of dieldrin, Y-HCH and 4-C-3-MPol. Significant biological degradation was concluded to have taken place for 4-C-3-MPol and pentachlorophenol since they exhibited poor association with sludge solids and on theoretical grounds are unlikely to be removed by air stripping.