Partial　Denitrification　(PD)　provides　a　new　route　for　nitrate-rich　wastewater　treatment　by　combining　with　energy-efficient　anammox.　This　process　was　reported　to　hardly　produce　N2O　despite　high　nitrite　accumulation　using　acetate　as　carbon　source.　This　study,　however,　demonstrated　significant　N2O　would　be　produced　when　feeding　with　real　municipal　wastewater,　the　NTR-N2O　(NO3−-to-N2O　transformation　ratio)　reached　as　high　as　10%.　The　supply　of　feed　with　a　high　COD/NO3−-N　ratio　was　unable　to　alleviate　N2O　production　but　was　severely　aggravated　after　nitrate　was　depleted.　Excess　carbon　source　resulted　in　accumulated　nitrite　further　being　reduced　with　NTR-N2O　largely　improved　to　63.4%.　Besides,　it　was　observed　that　acid　pH　inhibited　PD　activity　and　resulted　in　N2O　production　significantly　increased　with　the　NTR-N2O　of　39.9%　at　an　initial　pH　of　5.5.　The　increase　of　pH　to　alkaline　conditions　cannot　mitigate　N2O　production.　A　low　feeding　proportion　of　real　municipal　wastewater　for　low　nitrate　wastewater　treatment　can　drastically　lower　N2O　production.　The　NTR-N2O　was　only　0.1%　at　a　nitrate　concentration　of　10　mgN/L　(10%),　much　lower　than　that　at　30　mgN/L　with　a　30%　feeding　proportion　of　municipal　wastewater　(9.4%).　Complex　organics　and　ammonium　present　in　municipal　wastewater　were　supposed　to　be　the　primary　reasons　for　the　high　N2O　production.　Overall,　this　work　offered　a　new　insight　into　N2O　production　during　the　PD　process　using　the　complex　organics　from　wastewater　itself.　©　2023　Elsevier　Ltd