Improving stability and nitrogen removal performance of pilot-scale autotrophic process for mature landfill leachate treatment utilizing in-situ organics

[Display omitted] •A pilot-scale autotrophic process was set up to treat mature landfill leachate.•Excellent nitrogen removal (95.3%) was achieved without any organics input.•Using in-situ organics enhances stability & nitrogen removal of autotrophic process.•Poorly degradable organics could also be used by DNB to reduce NO3−-N residues. This study established a stable and efficient pilot-scale denitrification (DN) and partial nitritation (PN) combined with autotrophic nitrogen removal process for mature landfill leachate treatment. A total inorganic nitrogen removal efficiency (TINRE) of 95.3% was achieved without any external carbon source input, including 17.1%, 1.0% and 77.2% of nitrogen removal contributed by the DN, PN and autotrophic processes, respectively. ANAMMOX genus, Ca_Anammoxoglobus (19.4%) was dominant in autotrophic reactor. Moreover, denitrifying bacteria could utilize in-situ organics, including poorly degradable organics, to enhance the nitrogen removal performance of autotrophic process, contributing 3.4% of TINRE. This study provides new insights for the economical, low-carbon, and efficient treatment of mature landfill leachate.