Strategies for improvement of sludge quality and process performance of sequencing batch reactor plant treating municipal and tannery wastewater

Advanced process technology has been implemented at newly built wastewater treatment plants in Central and Eastern Europe. The wastewater treatment plant (WWTP) in Nowy Targ, Poland, the largest in Europe based on sequencing batch reactor (SBR) technology, has shown that newly constructed plants must be integrated into the system of water, wastewater, and sludge management in the city and the region. A significant supply of tannery wastewater with increasing chromium concentrations in the influent to the WWTP has resulted in many operational problems related mainly to sludge treatment. Evaluation of the process performance and sludge handling for 2 years of plant operation is presented. Efficient biological phosphorus removal with concentrations lower than 1 mg/l in effluent is obtained. Nitrogen removal is characterised by a low nitrification rate and a high denitrification rate. Problems with sludge handling are related to high excess sludge production, insufficient sludge stabilisation, low sludge dewatering efficiency and high chromium content in the sludge. Different strategies for sludge handling improvement are discussed. Sludge should be treated as a resource, which is recirculating in an eco-cycle with recovery of nutrients and energy. Such a process is proposed for the WWTP in Nowy Targ.