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Biological nitrification and denitrification of high ammonia landfill leachate using pre denitrification and pre/post denitrification processes Shiskowski, Dean Micheal


The purpose of this research was to investigate the nitrogen removal capabilities of two different biological process configurations treating high strength leachate containing up to 1200 mg N/1 of ammonia. The first configuration was a predenitrification system known as the Modified Ludzack- Ettinger (MLE) process. The MLE Startup Phase consisted of starting up two MLE systems treating "base" leachate containing about 230 mg N/1 of ammonia, followed by incrementally increasing leachate ammonia concentrations to a "target" level of 1200 mg N/1. Aerobic SRT's were maintained at 13 days during the MLE Startup Phase. Increases in clarifier sludge recycle flows to yield recycle ratios of 7:1 (System 1) and 8:1 (System 2), from 6:1, were investigated as a means to reduce effluent NOx concentrations during the MLE Recycle Phase. An aerobic SRT of 10 days was initially used in both systems during the MLE Recycle Phase. A pre and postdenitrification system, known as the Bardenpho process, was the second configuration evaluated. The Bardenpho Phase examined the overall nitrogen removal capabilities of this process when treating leachate containing about 1100 mg N/1 of ammonia. Both MLE systems experienced nitrification failure during the initial attempt to reach the "target" leachate ammonia concentration of 1200 mg N/1 (MLE Startup Phase). Anoxic methanol loadings were maintained at levels required for denitrifying the "base" leachate (i.e. 230 mg N/1). Rapid accumulation of ammonia in the systems, due to small amounts of anoxic ammonia assimilation caused by limited denitrification, apparently resulted in "free" ammonia toxicity of Nitrosomonas bacteria. Attempts to assimilate excess ammonia by increasing anoxic methanol loadings resulted in raising reactor pH levels, due to increased denitrification, and a further rise in "free" ammonia concentrations. Anoxic methanol loadings were increased simultaneously with leachate ammonia concentrations during the second attempt to reach the "target" ammonia concentration. Nitrification, and denitrification, was successfully established in both systems using this procedure. Increases in clarifier sludge recycle ratios (MLE Recycle Phase), with corresponding decreases in reactor actual hydraulic retention times, resulted in the rapid rise of reactor and effluent ammonia concentrations in both systems. Increases in aerobic SRT from 10 days to 20 days resulted in larger reactor solids levels and a reduction in effluent ammonia concentrations to around 50 mg N/1. Decreases in leachate ammonia concentration of about 80 mg N/1 resulted in effluent ammonia values of around 15 mg N/1. A total reduction in leachate ammonia concentration of about 200 mg N/1 did not further reduce effluent ammonia levels. Complete and consistent anoxic denitrification was achieved in both systems regardless of recycle ratio. Anoxic methanol loadings of about 2.8 mg COD/mg NOx-N resulted in 100% anoxic NOx removal. Aerobic NO₂/NOX ratios were about 0.60 in both systems. System 2 (r = 8:1) had significantly larger reactor solids levels than System 1 (r = 7:1) with slightly lower effluent total inorganic nitrogen (ammonia + NOx) concentrations (170 mg N/l versus 190 mg N/1). However, both systems had effluent total inorganic nitrogen concentrations of less than 160 mg N/l, when operating with recycle ratios of 6:1. Hence, increased total inorganic nitrogen removal was not realized when using larger recycle ratios. The Bardenpho System was capable of producing effluent containing less than 1 mg N/l of ammonia and 15 mg N/l of NOx, when treating 1100 mg N/l ammonia leachate. An Aerobic #1 SRT of 20 days was used with Aerobic #1 and clarifier sludge recycle ratios of 4:1 and 3:1, respectively. Residual effluent NOx was caused by incomplete ammonia removal in the first aerobic reactor and the production of NOx in the second aerobic reactor. However, approximately 5 mg N/l of ammonia was assimilated in the second anoxic reactor, thus indicating the need for a small amount of ammonia to remain in the mixed liquor so as to not limit denitrification. Anoxic methanol loadings of about 3.7 to 3.8 mg COD/mg NOx- N resulted in 100% anoxic NOx removal. Aerobic #1 NO₂/NOX ratios were about 0.60, with Aerobic #2 ratios < 0.09. The clarifier sludge recycle ratio had to be increased from 2:1 to 3:1, to prevent the accumulation of solids in the clarifier.

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