A　system　consisting　of　a　two-stage　up-flow　anaerobic　sludge　blanket　(UASB)　reactor　and　an　anoxic/aerobic　(A/O)　reactor　was　used　to　treat　municipal　landfill　leachate.　Denitrification　took　place　in　the　first　stage　of　the　UASB　reactor　(UASB1).　The　chemical　oxygen　demand　of　the　UASB1　effluent　was　further　decreased　in　the　second　stage　(UASB2).　Nitrification　was　accomplished　in　the　A/O　reactor.　When　diluted　with　tap　water　at　a　ratio　of　1:　1,　the　ammonia　nitrogen　concentration　of　the　influent　leachate　was　approximately　1200　mg.L-1,　whereas　that　of　the　system　effluent　was　approximately　8-11　mg.L-1,　and　the　corresponding　removal　efficiency　is　about　99.08%.　Stable　partial　nitrification　was　achieved　in　the　A/O　reactor　with　88.61%-91.58%　of　the　nitrite　accumulation　ratio,　even　at　comparatively　low　temperature　(16　degrees　C).　The　results　demonstrate　that　free　ammonia　(FA)　concentrations　within　a　suitable　range　exhibit　a　positive　effect　on　partial　nitrification.　In　this　experiment　when　FA　was　within　the　1-30　mg.L-1　range,　partial　nitrification　could　be　achieved,　whereas　when　FA　exceeded　280　mg.L-1,　the　nitrification　process　was　entirely　inhibited.　Temperature　was　not　the　key　factor　leading　to　partial　nitrification　within　the　16-29　degrees　C　range.　The　inhibitory　influence　of　free　nitrous　acid　(FNA)　on　nitrification　was　also　minimal　when　pH　was　greater　than　8.5.　Thus,　FA　concentration　was　a　major　factor　in　achieving　partial　nitrification.　(C)　2015　The　Chemical　Industry　and　Engineering　Society　of　China,　and　Chemical　Industry　Press.　All　rights　reserved.