Partial　denitrification　(PD,　nitrate　-＞　nitrite)　was　successfully　established　in　this　study　by　introducing　hydrolytic　acidification　(HA)　of　slowly　biodegradable　organic　matter　(SBOM).　A　high　selectivity　for　the　nitrate　over　nitrite　as　electron　acceptors　was　obtained　during　a　178-day　long-term　operation,　with　the　nitrate　to　nitrite　transformation　ratio　climbing　to　81.3%　at　an　influent　SBOM　of　286　mg/L　and　low-strength　nitrate　of　40　mg/L.　Acetate　(33.9%)　and　dissolved　saccharide　(19.3%),　as　the　major　SBOM　HA　products,　indeed　facilitated　high-efficiency　nitrite　production　by　serving　as　favorable　electron　donors.　This　was　well　explained　by　the　metagenomic　analysis　that　the　dominant　Dechloromonas　and　Thauera　denitrifying　genera,　which　hold　3.9　times　higher　abundance　of　nitrate　reductase　than　nitrite　reductase,　also　played　a　key　role　in　carbon　glycolysis　and　acidification.　This　study　provides　new　insight　into　PD　development　in　multiple　types　of　wastewater　for　the　versatile　carbon/nitrogen　metabolism　of　functional　bacteria.