The wastewater treatment plant (WWTP) in Nowy Targ, Poland, is the largest in Europe based on classical sequencing batch reactor (SBR) technology. The plant was completed in April 1995 as one of the essential elements in a program for the protection of the water quality in the Czorsztyn Reservoir. The process technology was designed for application to a typical municipal wastewater with a separate unit to treat tannery wastewater containing chromium. Experience from plant operation showed that the municipal wastewater inflow to the WWTP included tannery wastewater with increasing chromium concentrations, caused by poor wastewater management in the city. The average value in the influent was around 3 mg Cr/l (1996-1997) and showed an increasing trend. Investigations were focused on identification of the factors affecting the process performance. In this paper, evaluation of the treatment efficiency and process performance during 2 years of plant operation is presented, including studies of nitrification, denitrification and biological phosphorus removal. A cycle analysis was performed to investigate the reduction of different parameters during different phases of a cycle. Results of a sludge activity study based on OUR, AUR and NUR tests are presented and discussed.

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