Nitrous　oxide　(N2O)　production　during　the　partial　denitrification　process　with　nitrate　(NO3-N)　to　nitrite　(NO2-N)　transformation　ratio　of　80%　was　investigated　in　this　study.　Results　showed　that　N2O　was　seldom　observed　before　complete　depletion　of　NO3-N,　but　it　was　closely　related　to　the　reduction　of　NO2-N　rather　than　NO3-N.　High　COD/NO3-N　was　in　favor　of　N2O　production　in　partial　denitrification　with　high　NO2-N　accumulation.　It　was　seriously　enhanced　at　constant　acidic　pH　due　to　the　free　nitrous　acid　(FNA)　inhibition.　However,　the　N2O　production　was　much　lower　at　initial　pH　of　5.5　and　6.5　due　to　the　pH　increase　during　denitrification　process.　Significantly,　the　pH　turning　point　could　be　chosen　as　a　controlled　parameter　to　denote　the　end　of　NO3-N　reduction,　which　could　not　only　achieve　high　NO2-N　accumulation　but　also　decrease　the　N2O　production　significantly　for　practical　application.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.