Effects of total nitrogen and BOD₅/TN on anaerobic ammonium oxidation-denitrification synergistic interaction of mature landfill leachate in aged refuse bioreactor

Mature landfill leachate, featured with high ammonium (NH₄⁺) content and low biodegrade ability (low BOD₅/COD ratio), is hard to be treated. This study mainly focused on the effects of influent TN (total nitrogen) loading and BOD₅/TN ratios on the nitrogen removal efficiency of landfill leachate by landfill bioreactors. The results showed that when the influent total nitrogen loading was in the range of 15 g·(m³·d)^-1 to 25 g·(m³·d)^-1, the TN removal loading could remain stable between 10 g·(m³·d)^-1 and 12 g·(m³·d)^-1, while the TN removal efficiency decreased from 67.7% to 60.2% with the increasing loading. Therefore, TN loading shocks would lower the bioreactor's TN removal rate, but would not affect its TN removal loading. When the influent BOD₅/TN ratio was increased from 0.3 to 0.4 and the TN loading was controlled at 9 g·(m³·d)^-1, the TN removal rates were increased from 79.9% to 89.9% and 86.2% in anaerobic and aerobic, respectively. This implied that property enhancing BOD₅/TN ratio could significantly increase the TN removal efficiency of the bioreactor, and the effect was more significant under anaerobic condition. Analysis of nitrogen removal pathways showed that denitrification and anammox could take place synergistically in landfill bioreactor.