Prenitrification of Recycle Streams at Lincoln's Theresa Street Wastewater Treatment Facility

A prenitrification basin has been implemented at the Lincoln, Nebraska Theresa Street Wastewater Treatment Facility as part of recently completed plant improvements to obtain expanded nitrification capacity. The prenitrification basin is used for treatment of high strength recycle streams from solids processing operations. These streams, occurring intermittently, recycle approximately 30 to 40 percent of the ammonia received at the facility. Recycle streams are combined with a portion of return activated sludge in the aerated prenitrification basin resulting in a decrease of ammonia from over 500 mg/l in the recycle to 10 to 30 mg/l prior to combining with the main plant flow.The prenitrification basin has been successful and eliminating the shock load of the recycle streams and the ammonia bleed-through effect from these streams. Operational strategies are available to address performance optimization as well as alkalinity, pH, dissolved oxygen, and other environmental concerns. Approximately 80% ammonia removal has been obtained in the prenitrification basin with hydraulic detention times in the prenitrification basin as low as 3.2 hours.