A　novel　gravity　selector　was　firstly　introduced　between　the　aerobic　zone　and　clarifier　in　an　anaerobic/anoxic/oxic　(A(2)/O)　reactor　to　reduce　severe　filamentous　sludge　bulking　to　limited　filamentous　bulking　(LFB).　By　regulating　the　aeration　periods　of　operation　cycles　of　the　selector　and　other　parameters,　lighter　filamentous　bulking　sludge　was　gradually　washed　out,　reducing　the　sludge　volume　index　(SVI)　from　418　to　210　mL/g.　A　stable　LFB　state　was　achieved　in　80　d　with　pollutant　removal　efficiencies　of　90.1%,　93.7%,　87.9%　and　88.5%　for　COD,　NH4+-N,　TP　and　TN,　respectively.　Thiothrix　and　Beggiatoa,　with　extended　filaments,　dominated　the　filamentous　bacterial　population　of　the　first　phase,　whereas　Haliscomenobacter　hydrossis,　with　ingrown,　thin,　and　short　filaments,　dominated　the　LFB　state.　Therefore,　the　bulking　control　of　the　gravity　selector　relied　on　the　different　settling　velocities　of　bacteria　with　different　filament　morphologies　during　sedimentation　periods　in　the　gravity　field.　The　bacteria　with　long,　outstretched　filaments　settled　slowly　and　were　preferentially　washed　out　via　the　upper　outlet.　The　LFB　state　was　realised　at　low　DO　contents　of　0.5　similar　to　1.0　mg/L　and　a　long　sludge　retention　time　(SRT)　of　28　d　with　considerable　denitrifying　dephosphatation,　indicating　that　the　gravity　selector　can　improve　pollutant　removal　and　energy　utilisation.