Effects of an anaerobic zone in a textile wastewater treatment plant

High concentration of textile industries represents a serious environmental 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 overloaded, nitrification was not achieved. Therefore the plant flow sheet has been modified. The former predenitrification tank has been changed in an anaerobic compartment, since the internal recycle was stopped. The efficiency of the anaerobic reactor for COD removal, the selective pressure on the microbial community and the enhanced biological phosphorus 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 release 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, that suffers heavy filamentous bulking and Nocardia foaming). The final effluent PO4-P concentration was always lower than 1 mg L(-1).