The　novel　partial　denitrification　coupling　with　the　anammox　(PD/A)　process　is　emerging　as　a　promising　alternative　for　cost-efficient　nitrogen　removal　from　wastewater.　However,　it　encounters　challenges　of　competition　with　heterotrophic　denitrification　for　NO2--N　and　inhibition　of　complex　organic　carbon　involved　in　wastewater.　This　work　demonstrated　the　efficient　and　stable　nitrogen　removal　from　nitrate-containing　wastewater　(NO3--N　of　20-400　mg/L)　with　organic　carbon　from　domestic　wastewater　(NH4+-N　of　60.8　±　5.6　mg/L,　COD　of　195.6　±　58.4　mg/L)　by　a　single-stage　PD/A　process.　The　efficient　NO2--N　generation　was　achieved　by　utilizing　organic　carbon　in　domestic　wastewater.　With　the　feed　volume　ratio　of　nitrate-containing　wastewater　to　domestic　wastewater　(VNO3/Vdom)　decreasing　from　2.4/0.6　to　0.5/2.5,　the　removal　efficiency　of　NH4+-N　and　NO3--N　achieved　84.2%　and　98.3%,　respectively.　Anammox　bacteria　were　found　to　strongly　compete　over　denitrifying　bacteria　with　the　contribution　of　the　anammox　pathway　to　total　nitrogen　removal　as　high　as　91.6%.　Enhanced　competitiveness　of　anammox　bacteria　for　substrate　NO2--N　was　achieved　with　increasing　utilization　of　the　carbon　source　from　domestic　wastewater.　Metagenomic　analysis　revealed　that　the　electrons　produced　by　NADH　were　more　preferentially　transported　to　the　NO3--N　reductase　rather　than　the　NO2--N　reductase.　Therefore,　denitrifying　bacteria　Thauera　as　a　main　holder　of　Nar　genes　and　anammox　bacteria　Candidatus　Brocadia　jointly　removed　NO3--N　and　NH4+-N.　Sludge　granulation　with　increasing　domestic　wastewater　also　facilitated　the　efficient　retention　of　anammox　bacteria.　Overall,　this　study　highlighted　the　efficient　heterotrophic-autotrophic　cooperation　by　in　situ　utilization　of　the　complex　carbon　source　from　domestic　wastewater,　providing　valuable　technical　support　to　advance　the　PD/A　process　toward　practical　application.　©　2024　American　Chemical　Society.