In　this　study,　a　novel　strategy　for　nitritation　establishment　through　external　fermented　sludge　addition　is　proposed.　The　nitrifying　activities　under　various　fermentation　times　were　assessed;　batch　tests　results　revealed　that　the　decay　rate　of　nitrite　oxidizing　bacteria　(0.53　+/-　0.08　d-1)　was　much　higher　than　that　of　ammonia　oxidizing　bacteria　(0.15　+/-　0.04　d-1),　during　alkaline　fermentation　with　high　endogenous　free　ammonia　concentrations　(0.57-138.79　mgL-　1).　The　long-term　effects　of　fermented　sludge　addition　were　constantly　monitored　in　an　anaerobic/oxic/anoxic　sequencing　batch　reactor.　During　60　days　of　operation,　the　nitrite　accumulation　rate　reached　above　90%　and　could　be　maintained　stably.　Total　inorganic　nitrogen　removal　achieved　94.7%,　with　an　average　external　sludge　reduction　rate　of　61.3%,　after　incorporation　of　the　sludge　addition.　Illumina　MiSeq　sequencing　demonstrated　that　nitrite　oxidizing　bacteria　were　successfully　eliminated　and　the　relative　abundance　of　ammonia　oxidizing　bacteria　remained　at　0.39%,　resulting　in　nitrite　accumulation.