The　breakthrough　of　this　study　was　the　development　of　plug-flow　integrated　fixed-film　activated　sludge　(IFAS)　reactors　operated　with　alternating　anoxic/aerobic　(A(3))　conditions　for　enhanced　anammox　processes.　The　energy-saving　capacity　and　efficiency　of　this　A(3)-IFAS　system　was　compared　with　an　identical　IFAS　reactor　operated　with　continuous　low　oxygen　aeration　(CLOA)　through　a　test　period　of　141　days.　At　the　nitritation　start-up　phase,　the　nitrite　in　the　effluent　of　the　A(3)-IFAS　system　quickly　accumulated　to　77.9%,　which　was　higher　than　that　of　the　CLOA-IFAS　system　(61.7%).　The　A(3)-IFAS　system　reached　94.1　+/-　4.0%　of　total　inorganic　nitrogen　(TIN)　removal　in　the　stabilization　stage,　which　was　higher　than　that　in　the　CLOA-IFAS　system　(66.7　+/-　5.3%).　A(3)-IFAS　maintained　stable　partial　nitrification　and　TIN　removal,　whereas　the　nitritation　in　CLOA-IFAS　was　disturbed　on　the　96th　day　and　the　TIN　removal　became　unstable.　Quantitative　real-time　polymerase　chain　reaction　(qPCR)　analysis　indicated　that　ammonia-oxidizing　bacteria　(AOB)　were　dominant　in　both　IFAS　reactors,　while　the　amount　of　nitrite-oxidizing　bacteria　(NOB)　in　the　CLOA-IFAS　system　was　5.27　times　that　in　the　A(3)-IFAS　system.　The　kinetic　analysis　revealed　that　the　ratio　of　the　AOB　specific　growth　rate　(mu(AOB))　and　NOB　specific　growth　rate　(mu(NOB))　in　A(3)-IFAS　was　4.09,　which　was　higher　than　that　(3.1)　in　the　CLOA-IFAS　system,　implying　that　the　low　growth　rate　of　NOB　in　anoxic　zones　is　the　main　reason　for　the　stable　nitritation　and　high　TN　removal　in　A(3)-IFAS.