Anaerobic　ammonium　oxidation　(ANAMMOX)　is　a　recently　developed　process　to　treat　ammonia-rich　wastewater.　There　were　numerous　articles　about　the　new　technology　with　focus　on　the　ammonium-rich　wastewater　treatment,　but　few　on　advanced　municipal　wastewater　treatment.　The　paper　studied　the　anaerobic　ammonium　oxidation　(ANAMMOX)　process　with　a　down　flow　anoxic　biofilter　for　nitrogen　removal　from　secondary　clarifier　effluent　of　municipal　wastewater　with　low　COD/N　ratio.　The　results　showed　that　ANAMMOX　process　is　applicable　to　advanced　wastewater　treatment　with　normal　temperature　as　well　as　ammonia-rich　high　temperature　wastewater　treatment.　The　results　indicated　that　ammonia　removal　rate　was　improved　by　raising　the　nitrite　concentration,　and　the　reaction　rate　reached　a　climax　at　118.4　mgN/L　of　the　nitrite　nitrogen　concentration.　If　the　concentration　exceeds　118.4　mgN/L,　the　ANAMMOX　process　was　significantly　inhibited　although　the　ANAMMOX　bacteria　still　showed　a　relatively　high　reactivity.　The　data　also　indicated　that　the　ratio　of　NO2-　-N:　NH4+　-N　=　1.3:1　in　the　influent　was　appropriate　for　excellent　nitrogen　removal.　The　pH　increased　gradually　along　the　ANAMMOX　biofilter　reactor.　When　the　ANAMMOX　reaction　was　ended,　the　pH　was　tend　to　calm.　The　data　suggested　that　the　pH　could　be　used　as　an　indicator　to　describe　the　course　of　ANAMMOX　reaction.