In　this　study,　a　SNAD-SBBR　process　was　implemented　to　achieve　ammonia　removal　and　carbon　reduction　of　mature　landfill　leachate　under　extremely　low　dissolved　oxygen　conditions　(0.051　mg/L)　for　a　continuous　operation　of　266　days.　The　process　demonstrated　excellent　removal　performance,　with　ammonia　nitrogen　removal　efficiency　reaching　100　%,　total　nitrogen　removal　efficiency　reaching　87.56　%,　and　an　average　removal　rate　of　0.180　kg/(m3·d).　The　recalcitrant　organic　compound　removal　efficiency　reached　34.96　%.　Nitrogen　mass　balance　analysis　revealed　that　the　Anammox　process　contributed　to　approximately　98.1　%　of　the　nitrogen　removal.　Candidatus　Kuenenia　achieved　a　relative　abundance　of　1.49　%　in　the　inner　layer　of　the　carrier.　In　the　SNAD-SBBR　system,　the　extremely　low　DO　environment　created　by　the　highly　efficient　partial　nitrification　stage　enabled　the　coexistence　of　AnAOB,　denitrifying　bacteria,　and　Nitrosomonas,　synergistically　achieving　ammonia　removal　and　carbon　reduction.　Overall,　the　SNAD-SBBR　process　exhibits　low-cost　and　high-efficiency　characteristics,　holding　tremendous　potential　for　landfill　leachate　treatment.　©　2024　Elsevier　Ltd