EFFECTS OF AN ANAEROBIC ZONE IN A TEXTILE WASTE-WATER TREATMENT-PLANT

High concentration of textile industries represents a serious environm ental problem in the Como area in Northern Italy. The Seveso treatment plant was formerly performing biological removal of nitrogen by means of a modified Ludzack-Ettinger configuration. Being the plant overloa ded, nitrification was not achieved. Therefore the plant flow sheet ha s been modified. The former predenitrification tank has been changed i n an anaerobic compartment, since the internal recycle was stopped. Th e efficiency of the anaerobic reactor for COD removal, the selective p ressure on the microbial community and the enhanced biological phospho rus removal were evaluated. In the anaerobic tank 40% of the influent COD was removed with a reaction time of only 45 minutes. The activated sludge showed a very high presence of Poly-P bacteria; anaerobic P re lease was noticed during the anaerobic phase. Sludge settleability was always good (contrary to a similar activated sludge treatment plant, also treating textile wastewater but without an anaerobic selector, th at suffers heavy filamentous bulking and Nocardia foaming). The final effluent PO4-P concentration was always lower than 1 mg L(-1).