Optimization of operating parameters of intermittent aeration-type activated sludge process for nitrogen removal: a...

Biological nitrogen removal is becoming a proven approach to reducing the total nitrogen discharged from wastewater treatment facilities. Simulation performed with intermittent aeration-type activated sludge process using Activated Sludge Model No. 1 predicted that up to 90% total nitrogen removal could be attained when the total cycle time and its anoxic phase were balanced adequately. This control limits electron donor and acceptor levels--ammonia-nitrogen (NH4(+)-N) in the aerobic phase and nitrate-nitrogen (NO3(-)-N) in the anoxic phase. Specifically, maximum nitrogen removal appears to be achieved with a 2- to 3-hour cycle time, during which, anoxic conditions were present for 40 to 50% of the time. A 10- to 16-hour hydraulic retention time appears adequate to achieve these results. The solids retention time studied was between 15 and 25 days, as this range was deemed sufficient to establish the nitrifying organism population in most applications. Predictions indicate that the conventional activated sludge system can be retrofitted for better nitrogen management at the treatment plants.