PRINCIPLES IN THE DESIGN OF SINGLE-SLUDGE ACTIVATED-SLUDGE SYSTEMS FOR BIOLOGICAL REMOVAL OF CARBON, NITROGEN, AND PHOSPHORUS

The function of the single-sludge activated-sludge system has expanded from chemical oxygen demand (COD) removal to include, progressively, nitrification, denitrification, and phosphorus removal, all biological . With such complexity, design procedures based on fundamental behavio ral patterns are required. The fundamental principles of a steady-stat e model for biological excess phosphorus removal (BEPR) that is based on the current understanding of the mechanisms of BEPR are described. The model can be used for design and to predict the expected system re sponse under constant flow and load conditions. With the aid of the mo del, the influence of various parameters on the magnitude of phosphoru s removal and the interactions between BEPR and nitrification and deni trification are examined, Principle variables that influence phosphoru s removal are an influent wastewater characteristic-readily biodegrada ble chemical oxygen demand concentration-and process design parameters -anaerobic mass fraction and its subdivision and sludge age. Also, the model indicates that, in agreement with observations, preventing recy cling of nitrate to the anaerobic reactor is one of the main considera tions in design.