Partial-denitrification　(nitrate　to　nitrite)　can　supply　nitrite　for　anammox　which　can　reduce　organic　matter　consumption　in　wastewater　treatment　plants　(WWTPs).　In　order　to　achieve　stable　partial-denitrification,　the　effect　of　pH　on　denitrification　were　investigated　for　420　days　in　three　reactors　with　influent　pH　of　5.0,　7.0　and　9.0.　The　results　indicate　that　the　nitrite　accumulation　rate　(NAR)　increased　with　pH,　with　average　effluent　NARs　being　21%,　38%　and　57%　in　the　above　reactors,　respectively.　The　sludge　cultivated　at　a　high　pH　of　9.0　was　resistant　to　pH　shock,　with　a　high　NAR　being　maintained　at　83%　when　it　was　exposed　to　a　low　pH　of　5.0.　Metagenomic　analysis　showed　that　the　higher　NAR　at　pH　9.0　was　correlated　with　an　enrichment　of　Thauera,　which　harbored　more　nitrate　reductase　(8098　hits)　than　nitrite　reductase　(2950　hits).　Based　on　these　findings,　a　novel　process　was　proposed　for　achieving　partial-denitrification/anammox　in　mainstream　WWTPs.