Full-scale evaluation of biological nitrogen removal in the step-feed activated sludge process

Establishment of nitrification and denitrification in an existing conventional, step‐feed activated sludge plant designed for suspended solids and carbonaceous biochemical oxygen demand removal was evaluated in a full‐scale study at the Tallman Island Water Pollution Control Plant in New York City. One of four biological treatment batteries consisting of an aeration tank and two rectangular secondary clarifiers was isolated from the rest of the plant and was used for the study. Nitrification rates and their temperature dependency were determined using NH 3 ‐N and NO 3 ‐N profiles developed along the aeration tank during the summer and winter months. The data suggested the occurrence of simultaneous nitrification and denitrification in the aeration tank. Virtually complete denitrification was observed within the sludge blanket of the secondary clarifier.