The effect of ammonial loading, solids retention time and operating temperature on the biological nitrification and denitrification of high ammonia landfill leachate

• Main Author: Azevedo, Barry
• Format: Others
• Language: English
• Published: 2008
• Online Access: http://hdl.handle.net/2429/2630

The effect of ammonia loading, solids retention time and operating temperature (20, 17, 14, 12 and 10 °C) on the treatment of high ammonia landfill leachate (200, 300, 600, 1000, 1500 and 2000 mg NH4-N/L), was investigated. Two biological, single-sludge, nitrification-predenitrification systems were operated in parallel; one with a 10 day aerobic SRT, and the other with a 20 day aerobic SRT. The study consisted of two phases: an ammonia loading phase and a cold temperature phase. From the ammonia loading phase, it was found that at an influent leachate ammonia level of 1500 mg N/L, both systems produced an effluent of <1 mg NH4-N/L and approximately 170 mg NO.--N/L. Aerobic nitrite accumulation was observed and was likely a factor in a parallel decrease in the COD:NOx ratio from approximately 6:1 to 4:1. At the leachate ammonia level of 1500 mg N/L, "free" ammonia levels in the anoxic reactor were estimated to have been 20 mg N/L. This elevated anoxic "free" ammonia level did not appear inhibitory to either the ammonia oxidizers (Nitrosomonas) or to the denitrifiers, but may have inhibited nitrite oxidizers (Nitrobacter), thereby resulting in nitrite accumulation. When the influent ammonia concentration was raised from 1500 to 2000 mg N/L, nitrification in both systems was observed to decrease from 100 % to approximately 20 %. Several factors may have contributed to the failure of nitrification including: insufficient dissolved oxygen, solids/foaming problems, and levels of anoxic "free" ammonia inhibitory to Nitrosomonas. During the cold temperature phase, the temperature was decreased from 20 to 10 °C while maintaining the simulated leachate ammonia level at 1500 mg N/L. Aerobic nitrite accumulation and rising aerobic BOD5 was observed to begin at 14 °C. When the temperature was decreased from 12 °C to 10 °C, nitrification was observed, in both SRT systems, to decrease from approximately 95 % to approximately 20 %. In the 10 day SRT system, denitrification decreased from 99 % to30 %; in the 20 day SRT system, denitrification decreased from 99 % to 82 %. Based on the rise of aerobic nitrite, and only partial failure of denitrification, cold temperature was deemed responsible for nitrification failure, which for the 10 day SRT system, subsequently precipitated the failure of denitrification. In both awstems, nitrification was re-established at 10 °C, by ceasing to waste solids and by stopping methanol addition. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate