Not Your Normal Nitrates Nitrite Problems in Rerate Pilot Testing Result in Innovative BNR Step Feed Process

The Arlington East Water Reclamation Facility is one of five regional facilities owned and operated by JEA. In addition to planning for additional wastewater flow projections, JEA has proposed a voluntary nitrogen load reduction goal from its treatment facilities of 50% from the 1999 baseline by the year 2007. The facility will be required to reduce nitrogen discharges in the future due to the TMDL currently being performed on the receiving water body. The Arlington East Facility was chosen for performing initial full scale pilot testing and stress testing work to verify that the facility could adequately treat additional flow and to investigate potential biological nitrogen removal processes and their performance. At the conclusion of the study, a permit application for a rerated capacity of 25 mgd was assembled resulting in an increase in the rated capacity of 5 mgd without additional tankage.Several full-scale pilot trials of nitrogen removal process configurations were tried at the plant in 2002 and early 2003, with varying levels of total nitrogen reduction. A more detailed approach was followed in 2003 including development of a calibrated process model and special plant monitoring and intensive sampling campaign under re-rated design flows and loads.To further refine the modeling and obtain more full-scale data the plant was placed in the nitrification mode under the proposed re-rated capacity by taking half of the aeration basins and secondary clarifiers offline. However, during this testing a significant chlorine demand problem was encountered due to the presence of nitrite in the secondary effluent resulting from partial nitrification (up to 6 mg/L). To reduce the nitrite problem plant personnel initiated a set of varying quasi “anoxic zones” and ran the plant in a step aeration mode. The nitrite in the secondary effluent decreased significantly and the chlorine demand problem was resolved. In addition, the effluent total nitrogen goal was met under this new operating mode. The full-scale pilot/stress testing along with the calibrated modeling resulted in a novel solution for achieving biological nitrogen removal by using an unorthodox step aeration process. These results were utilized to determine the optimum BNR configurations for the future plant upgrade.