Activated Sludge Nitrification in Temperate Climate

Abstract

In Denmark winter temperature of the wastewater is typically 5-10°C, and ammonia concentrations below 1-4 mg/l are normal discharge limits under these conditions. Special attention is needed in design and operation of treatment plants in order to fulfill such limits. Based on a simple energy balance a steady-state temperature model is developed and verified at full scale treatment plants. The model enables a good estimate of expected winter temperatures in the design phase. Deep tanks and good protection against wind exposure are shown to be attractive means to avoid a too low process temperature during winter periods. Successful winter nitrification can be obtained if the plant operator is supplied with tools to identify arising problems. A procedure to predict if the actual plant nitrification capacity is approaching the necessary capacity based on the load is described and tested.