Anaerobic　ammonium　oxidation　(anammox)　has　attracted　extensive　attention　as　a　potentially　sustainable　and　economical　municipal　wastewater　treatment　process.　However,　its　large-scale　application　is　limited　by　unstable　nitrite　(NO2--N)　production　and　associated　excessive　nitrate　(NO3--N)　residue.　Thus,　our　study　sought　to　evaluate　an　efficient　alternative　to　the　current　nitritation-based　anammox　process　substituting　NO2--N　supply　by　partial-denitrification　(PD;　NO3--N　-＞　NO2--N　)　under　mainstream　conditions.　Ammonia　(NH4+-N)　was　partly　oxidized　to　NO3--N　and　removed　via　a　PD　coupled　anammox　(PD/A)　process　by　mixing　the　nitrifying　effluents　with　raw　wastewater　(NH4+-N　of　57.87　mg　L-1,　COD　of　176.02　mg　L-1).　Excellent　effluent　quality　was　obtained　with＜　5　mg　L--(1)　of　total　nitrogen　(TN)　despite　frequent　temperature　fluctuations　(25.7-16.3　degrees　C).　The　genus　Thauera　(responsible　for　PD)　was　the　dominant　denitrifiers　(36.4%-37.4%)　and　coexisted　with　Candidatus　Brocadia　(anammox　bacteria;　0.33%-0.46%).　The　efficient　PD/A　allowed　up　to　50%　reduction　in　aeration　energy　consumption,　80%　decrease　in　organic　resource　demand,　and　lower　nitrous　oxide　(N2O)　production　compared　to　conventional　nitrification/denitrification　process.　Our　study　demonstrates　that　coupling　anammox　with　flexible　NO2--N　supply　has　great　potential　as　a　stable　and　efficient　mainstream　wastewater　treatment.