The Behaviour of Chlorinated Organics during Activated Sludge Treatment and Anaerobic Digestion

An activated sludge pilot plant was operated at 4,6 and 9d sludge ages with influent settled sewage from a full scale treatment works. The behaviour of the chlorinated organic micropollutants was examined at their background levels in sewage and significant removal was seen for dieldrin, Y-HCH, DDE, PCB and 2,4-DCPol at all sludge ages. Dieldrin, Y-HCH, DDE PCB, 2,4,5-TCPol, 2,4,6-TCPol and 2,4-DCPol were found to associate with activated sludge solids. 2,4-DCPol and 4-C-2MPol were found to be biologically degraded. Mixed primary sludge from the same sewage treatment works was incubated anaerobically with and without azide addition to prevent biological activity. Rapid removal of Y-HCH was concluded to be due to chemical degradation, while biological activity was concluded to be the mechanism for the removals of 2,4-D, 2,4,5-T, 2,4,6-TCPol and 2,3,4,6-TeCPol. Statistically significant increases were observed for 2,3,4,6-TeCPol in azide treated incubations and for 2,4,5-TCPol and 2,4-DCPol in both treated and untreated anaerobic sludges.