A　novel　biological　system　coupling　an　UASB　and　a　SBR　was　established　to　treat　landfill　leachate.　In　order　to　enhance　organics　and　nitrogen　removal,　simultaneous　denitritation　and　methanogenesis　(SDM)　was　performed　in　the　UASB.　Free　ammonia　(FA)　inhibition　on　nitrite-oxidizing　bacteria　(NOB)　and　process　control　was　used　to　achieve　nitrite　pathway　in　the　SBR.　Results　over　623　days　showed　that　the　maximum　organic　removal　rate　in　the　UASB　and　the　maximum　ammonium　oxidization　rate　in　the　SBR　was　12.7　kgCOD/m(3)　d　and　0.96　kgN/m(3)　d,　respectively.　The　system　achieved　COD,　TN,　and　NH4+-N　removal　efficiencies　of　93.5%,　99.5%,　and　99.1%,　respectively.　By　using　FA　inhibition　coupled　with　process　control,　the　nitrite　pathway　was　started-up　in　the　SBR　at　low　temperatures　(14.0-18.2　degrees　C)　and　was　maintained　for　142　days　at　temperatures　below　15　degrees　C　(the　lowest　level　was　9.0　degrees　C).　The　predominant　ammonia-oxidizing　bacteria　(AOB)　explains　essentially　stable　nitritation　obtained.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.