Feasibility of wastewater treatment plant upgrade by enhanced biological phosphorus removal: case study Koprivnica, Croatia

This paper reports on the preliminary tests carried out to characterize the wastewater and the activated sludge from a sequencing batch reactor (SBR) municipal wastewater treatment plant (WWTP) to evaluate possibility of introduction of enhanced biological phosphorus removal (EPBR) into the plant. Wastewater which was treated at the WWTP was municipal wastewater of medium strength, with some peak organic loads due to industrial discharge. Operating conditions were often changed in order to satisfy effluent discharge requirements. Biological methods for sludge characterisation including anaerobic P-release test, aerobic P-uptake test and anoxic P-uptake test were used to determine the presence of polyphosphate accumulating organisms (PAO) within the sludge of the WWTP, along with nitrification and denitrification tests. Anaerobic phosphorus release rate on acetate was low 0.19-2.41 mgP/gVSS*h. Aerobic P-uptake rate was in all our tests lower than 1.0 mg P/gVSS*h and anoxic P-uptake was lower than 0.63 mgP/gVSS*h. EPBR could not be achieved with the activated sludge from the plant but it may be possible, after introducing optimal conditions and regime.