Evolution of the Southpest Wastewater Treatment Plant

The treated effluent of the Southpest Wastewater Treatment Plant is dischar ged into a small, low-flow branch of the Danube susceptible to eutrophicati on. The first, high-load activated sludge system with a hydraulic retention time of 2.5 hrs in the aerated basins, was installed here in 1966. The pap er presents the evolution of the technology by illustrating the effects of the different changes carried out since 1991. Reconfiguration of the existing activated sludge basins connected originall y in parallel into an arrangement of tanks in series increased the settleab ility of the sludge as well as the efficiency of COD removal significantly. Introduction of an anaerobic zone preceding the aerated basins facilitated biological excess phosphorus removal with a consequent release in the thic kener and digester. Introducing lime addition into the recycled sludge proc essing wastes significantly improved the performance of the system. However , since there had been no provision built for eliminating the nitrate conte nt of the recycled sludge, efficiency of phosphorus removal proved to be de pendent on the eventually occurring nitrification. In order to achieve both an effective nitrogen and phosphorus removal the c urrent technology established in 1999 applies a nitrification and a denitri fication filter following the activated sludge unit and uses precipitation for phosphorus removal.