FULL SCALE RERATE PILOT TESTING RESULTS IN AN INNOVATIVE BNR STEP FEED PROCESS AND ENR NITROGEN LEVELS

The Arlington East Water Reclamation Facility is one of five regional facilities owned and operated by JEA. Because of the high population growth rate of the City of Jacksonville, JEA is investigating all of its wastewater treatment facilities for potential plant rerating. In addition to planning for additional wastewater flow projections, in 2001 JEA proposed a voluntary 50% nitrogen load reduction goal from its treatment facilities by the year 2007. These two goals required that the Arlington East Facility, which currently has no nitrogen permit limit, meet a total nitrogen concentration of 6 mg/L while at the same time rerating the plant from 20 to 25 mgd. In addition, JEA desired to achieve these goals without construction of additional basins. Comprehensive wastewater characterization, BioWin modeling, and full-scale pilot testing and stress testing work was conducted to verify that the facility could adequately treat additional flow and to investigate potential biological nitrogen removal processes to meet the total nitrogen goal of 6 mg/L.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 upgrades. The full-scale pilot/rerating testing showed excellent total nitrogen removal under the high loading conditions and verified the ability to rerate the facilities. This testing demonstrated the benefits of the combination of higher carbon loading and elevated MLSS on total nitrogen removal by quickly reducing D.O. in the anoxic zones and promoting simultaneous nitrification/denitrification.Recently, JEA learned that the proposed TMDL on the receiving stream would result in required effluent TN levels of 3 to 4 mg/L. The results of the full scale testing and calibrated BioWin model were used to develop and effectively evaluate options for achieving enhanced nitrogen removal (ENR) TN limits at the Arlington East Facility.