Achieving　the　anammox　process　in　suspended　sludge　system　without　supplementing　carriers　or　inoculating　anammox　bacteria　is　a　challenging　topic,　especially　inmunicipal　wastewater　treatment.　Long-termmaintenance　of　partial　nitrificationwas　realized　in　this　study　bymaintaining　dissolved　oxygen　(DO)　below0.5　mg/L,　by　using　a　DO　meter　and　controlling　the　oxygen　diffuser　apparatus　in　anaerobic-aerobic-anoxicmode　in　a　sequencing　batch　reactor,　leading　to　successful　enrichment　of　anammox　bacteria.　Under　134　maintenance　days　of　partial　nitrification　with　an　average　nitrite　accumulation　rate　of　94.5%,　anammox　bacteria　gradually　enriched　in　suspended　sludge　with　an　increasing　relative　abundance　from　0%　on　18th　day　to　0.44%　on　124th　day,　and　the　nitrogen　removal　efficiency　improved　from　30%　to　85%.　(NO2-)-N-15　N　isotope　labeling　test　showed　that　activities　of　anammox　and　denitrification　were　1.48　and　1.22　mu　molN/(gVSS.h),　respectively.　The　contribution　of　anammox　in　the　anoxic　stage　to　nitrogen　removal　was　20%,　but　anammox　N　removal　continued　in　the　aerobic　stage,　as　well.　Long-term　maintenance　of　partial　nitrification　and　lowdissolved　oxygen　levelswere　the　key　factors　leading　to　enrichment　of　anammox　bacteria.　(C)　2021　Elsevier　B.V.　All　rights　reserved.