This　study　tested　the　feasibility　of　plug-flow　integrated　fixed-film　activated　sludge　(IFAS)　reactor　in　applying　sewage　partial　nitritation/anammox　(PN/A)　process.　The　IFAS　reactor　was　fed　with　real　pretreated　sewage　(C/N　ratio　=　1.3)　and　operated　for　200　days.　High　nitrogen　removal　efficiency　of　82%　was　achieved　with　nitrogen　removal　rates　of　0.097　+/-　0.019　kg　N/(m(3).d).　Therefore,　plug-flow　IFAS　reactor　could　be　an　alternative　to　applying　sewage　PN/A　process.　Besides,　it　was　found　that　the　stability　of　sewage　PN/A　process　was　significantly　affected　by　residual　ammonium.　Nitrate　accumulated　in　effluent　and　PN/A　performance　deteriorated　when　residual　ammonium　was　below　1　mg/L.　On　the　contrary,　long-term　stable　PN/A　operation　was　achieved　when　residual　ammonium　was　over　3　mg/L.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.